sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

revised age of the late neogene terror bird titanis in north america during the great american interchange the giant flightless terror bird titanis walleri is known from florida and texas during the late neogene the age of t walleri is problematic because this taxon co occurs with temporally mixed i e time averaged faunas at two key sites thus prior to this study t walleri from the santa fe river florida type locality was either as old as late pliocene ca 2 2 ma or as young as latest pleistocene ca 15 ka likewise t walleri from the nueces river texas was either early pliocene ca 5 ma or latest pleistocene ca 15 ka in order to better resolve this age range the rare earth element ree patterns of t walleri from the santa fe river florida were compared to two biochronologically distinctive groups late pliocene versus late pleistocene of fossil mammals from the same locality similarly the ree patterns of t walleri from texas were compared to two groups early pliocene versus latest pleistocene of fossil mammals from the same locality the ree patterns of t walleri from florida are indistinguishable from those of the co occurring late pliocene mammals likewise the ree pattern of t walleri from texas is indistinguishable from those of the co occurring early pliocene mammals given these ree constraints the revised age of t walleri is early pliocene in texas ca 5 ma and late pliocene ca 2 2 1 8 ma in florida as such t walleri is interpreted as an early immigrant during the great american interchange prior to the formation of the isthmian land bridge no evidence currently exists for pleistocene t walleri in north america

models of diffusion limited uptake of trace elements in fossils and rates of fossilization abstract many fossils are assumed to take up trace elements by a process of combined diffusion plus adsorption da yet in principle composition profiles can be explained by several different diffusion limited processes including diffusion plus reaction or recrystallization dr and double medium diffusion dmd the da and dmd models are supported by ree and u composition profiles across fossil teeth measured by laser ablation icp ms that show error function like diffusion profiles into enamel from the dentine enamel interface and concentrations in the interior of enamel that are at original biogenic levels or higher published composition and age profiles in some pleistocene bones may be better explained by a dr model all three diffusion models imply linear behavior between age and distance squared vastly simplifying u series dating methods for pleistocene fossils modeled uptake rates for fossil teeth yield a strict minimum bound on durations of about one decade to one century the similarity of diffusion profiles in teeth irrespective of depositional ages ranging from 30 ka to 30 ma implies that uptake occurred quickly with a maximum duration of a few tens of kyr for typical fossil enamel faster uptake is implied for typical fossil bone and dentine disparities in these uptake estimates compared to some archeological bone may reflect sampling and preservation bias for paleontological vs archeological materials

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

magmatic processes revealed by textural and compositional trends in merapi dome lavas syn eruptive degassing of volcanoes may lead to syn eruptive crystallization of groundmass phases we have investigated this process using textural and compositional analysis of dome material from merapi volcano central java indonesia samples included dome lavas from the 1986 88 1992 93 1994 and 1995 effusive periods as well as pyroclastic material deposited by the november 1994 dome collapse with total crystallinities commonly in excess of 70 phenocrysts 1 microlites the liquids present in merapi andesites are highly evolved rhyolitic at the time of eruption feldspar microlites in dome rocks consist of plagioclase cores ab63an29or8 surrounded by alkali feldspar rims ab53an5or42 compositional pairs which are not in equilibrium a change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition a small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites suggesting that the 1994 collapse event incorporated less degassed partially liquid magma in addition to fully solidified dome rock as decompression drives volatile exsolution rates of degassing and resultant microlite crystallization may be governed by magma ascent rate microlite crystallinity is nearly identical among the 1995 dome samples an indication that similar microlite growth conditions ph2 o and temperature were achieved throughout this extrusive period however microlite number density varied by more than a factor of four in these samples and generally increased with distance from the vent low vent ward microlite number densities and greater microlite concentrations down flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density suggesting that extrusion slowed during 1995 crystal textures and compositions in the 1992 93 and 1994 domes share the range exhibited by the 1995 dome suggesting that transitions in crystallization conditions i e rates of undercooling determined by effusion rate are cyclic q 2000 elsevier science b v all rights reserved

oxygen isotopic composition of fossil horse tooth phosphate as a record of continental paleoclimate abstract oxygen isotopic elemental and x ray data are presented for a suite of 24 fossil horse teeth from nebraska ranging in age from 18 2 to 8 5 ma to test the use of 18o of enamel phosphate 18op04 as a quantitative record of continental climate modern equid teeth were analyzed to estimate a relationship between 8op04 and environment water multiple samples of seven different fossil species from burge quarry a 12 ma attritional fossil deposit indicate the diagenetic overprints exist but can be detected by decreased p concentration and increased crystallinity relative to modern enamel isotopic variation for the pristine samples from burge quarry is 1 5 1 n 9 which may represent the resolution of the procedure within a stratigraphic horizon there are no apparent correlations with body size hypsodonty or phylogeny a range of 7 0 in 18op04 occurs over the 10 m y interval a trend towards depleted 18op04 of about 4 corresponds to a depletion of up to 6 0 in 18o of precipitation between 18 2 and 8 5 ma but the range of variation of burge is large relative to the climate signal our results demonstrate that 18op04 should be useful in quantitatively reconstructing cenozoic continental paleoclimate on 106 year timescales isotopic variation due to taphonomic bias and the terrestrial rock record will likely obscure higher order climate signals

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

earliest art in the americas incised image of a proboscidean on a mineralized extinct animal bone from vero beach florida abstract a fragmented fossil bone incised with the figure of a proboscidean was recently found at vero beach florida near the location where late pleistocene fauna and human bones were recovered from 1913 to 1916 this engraving may represent the oldest and only existing example of terminal pleistocene art depicting a proboscidean in the americas because of the uniqueness rarity and potential antiquity of this specimen caution demanded that a variety of tests be used in an attempt to verify its authenticity the mineralized bone was identified as mammoth mastodon or giant sloth rare earth element analysis was consistent with the fossil bone being ancient and originating at or near the old vero site 8 ir 9 forensic analysis suggests the markings on the bone are not recent optical microscopy results show no discontinuity in coloration between the carved grooves and the surrounding material indicating that both surfaces aged simultaneously scanning electron microscopy sem revealed that the edges of the inscription are worn and show no signs of being incised recently or that the grooves were made with metal tools in addition the backscattered sem images suggest there is no discontinuity in the distribution of light and heavy elements between the scribed region and the surrounding bone indicating that both surfaces aged in the same environment this is very different from an intentional mark made on the bone for comparison energy dispersive x ray spectroscopy edxs shows that the surface contains significant amounts of calcium phosphorus oxygen and carbon typical of a mineralized bone surface examination of a cast and mold of the incised bone by reflectance transformation imaging rti also provided no evidence that the engraving was made recently all of these results are consistent with the mammoth engraving being authentic

accumulation of sediments trace metals pb cu and total hydrocarbons in narragansett bay rhode island abstract the accumulation of sediments trace metals and hydrocarbons has been estimated from the analysis of the sediment from six coring sites in narragansett bay radionuclides 234 th xs 210 pb xs 239 240 pu with known input functions and trace metals cu pb were used we estimate that 6 9 10 4 tons of sediments 51 90 tons of pb 72 100 tons of cu and 400 1000 tons of total hydrocarbons accumulate annually under present conditions in the bay this represents 64 117 pb 89 123 cu and 23 58 hydrocarbons respectively of present day inputs to the bay furthermore close to 100 of the particle reactive radionuclides 210 pb and 239 240 pu accumulate in the bay present day inputs to the bay were calculated independently as 77 80 tons pb and 81 tons of cu sewage effluents were the dominant source of cu whereas atmospheric deposition and urban runoff were most important for pb dredging activities by the u s army corps of engineers between 1946 and 1971 removed more sediments from the bay than would have accumulated during the same time in the undredged areas of the bay copper smelting and coal mining on the shores of the upper bay during 1866 1880 left an imprint in the sediments which is still evident model derived accumulation rates of pb cu and coal during that time were 3 4 times present day inputs

sulphide speciation in surface sediments of the lagoon of venice a geochemical and mineralogical study abstract three 1 m cores of recent sediments from the lagoon of venice were sampled to obtain the vertical distribution of fe zn cu pb and cd and to study authigenic iron sulphides from the geochemical and mineralogical viewpoints zn cu pb and cd occur in superficial sediments in concentrations many times higher than those of their natural background the existence of zn cd and cu pb couples were revealed by their very similar depth profiles the latter couple is also closely correlated with sulphide sulphur iron is characterized by quite a different behaviour showing a sharp increase at a depth of 35 cm from a geochemical viewpoint authigenic sulphides were distinguished into pyrite and acid volatile sulphides greigite and mackinawite their distribution is characterized by high concentrations of avs in the first 25 cm of sediments dramatically decreasing with depth pyrite present in lower amounts shows the opposite trend although in one core both species were present in comparable amounts mineralogical study of the heavy mineral fraction revealed that the iron sulphides are composed of pyrite organised both in the classic framboidal growth and in unordered micro crystal swarms and iron mixed sulphide aggregates with variable optical patterns and colloform botroidal or massive growth no heavy metals were detected in the crystalline lattice of the sulphides down to 25 cm all types of sulphides occur and with increasing depth pyrite clearly prevails this behaviour may have various causes e g chemico physical control by specific microniches temporal and spatial variations favouring the formation of different types evolution of iron mixed sulphides into more stable forms

provenancing of hominid and mammalian fossils from kanjera kenya using edxrf abstract we describe a rapid non destructive energy dispersive x ray fluorescence edxrf technique for provenancing fossil bone and apply it to surface collected fossils from kanjera kenya the locality is best known for its controversial anatomically modern human fossils potentially among the earliest from africa excavations of the 1987 1988 smithsonian expedition provided the in situ fossil sample necessary to provenance the previous finds relative sr y zr u rb rn and th concentrations were used to characterize 301 fossils from six stratigraphic units the sources of the surface fossils important fossils from past kanjera expeditions including the hominid and theropithecus oswaldi samples were analysed and their relative elemental values used to assign them to a reference sample the hominids post date kanjera formation deposition the t oswaldi fossils are largely attributable to the early pleistocene kanjera bed kn 2a secondary deposition of kanjera formation fossils into later strata was noted

heterogeneous rare earth element ree patterns and concentrations in a fossil bone implications for the use of ree in vertebrate taphonomy and fossilization history abstract a bone fragment cgdq 3 of falcarius utahensis a therizinosaur from the early cretaceous cedar mountain formation utah contained within a carbonate nodule was analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms in order to investigate ree variability within a thin walled phalanx previous studies have found depth related ree pattern variations however in cgdq 3 variation occurs along the circumference of the bone nasc normalized ree patterns and concentrations vary between two apparent end members a light ree enriched lree pattern similar to solution icp ms analysis of this bone characterizes approximately two thirds of the bone fragment total ree concentrations are high and do not vary significantly from the periosteal surface to the medullar surface conversely the remaining one third of the bone has ree patterns that are mree depleted and low in total ree concentrations ree concentrations in this part of the bone do not vary significantly from the periosteal to the medullar surface a positive ce anomaly is found throughout the entire bone and is greatest within the lree enriched portion of the bone this in combination with the lree enrichment suggests that the bone fossilized under reducing conditions the distance between the lree enriched and mree depleted regions is less than 1 mm isotopic and petrographic analyses of the bone and surrounding carbonate matrix suggest the ree patterns in the bone were the result of partial fossilization incomplete filling of micro pore spaces around bone crystallites in an environment with changing redox conditions the lower mree depleted part of the bone fossilized contemporaneously with a pendant cement that formed on the underside of the bone in the vadose zone formation of the pendant cement restricted water flow through the bone isolating the lower portion which incorporated a mree depleted pattern the upper part of the bone lree enriched side fossilized under more reducing conditions than the lower part this resulted in reductive dissolution of minerals such as hydrous ferric oxides and manganese oxides which were lree enriched with positive ce anomalies these ree were then incorporated into the upper part of the bone this likely occurred after the bone entered the saturated zone below the water table the thinness of the bone and presence of a pendant cement helped facilitate partial fossilization of the bone preserving the ree signature of an earlier fluid as demonstrated by this case study differences in ree patterns within a fossil may record changes in geochemical conditions during fossilization particularly when bones are encased in a material that reduces fluid permeability such as micritic vadose calcite analysis of such bones may offer the opportunity to decipher complex fluid histories that occur during fossilization la icp ms should be utilized to confirm solution icp ms analysis if it yields high ree variability prior to an interpretation of reworking or time averaging

heavy metal contamination of coastal lagoon sediments by anthropogenic activities the case of nador east morocco nador lagoon sediments east morocco are contaminated by industrial iron mine tailings urban dumps and untreated wastewaters from surrounding cities the lagoon is an ecosystem of biological scientific and socio economic interests but its balance is threatened by pollution already marked by biodiversity changes and a modification of foraminifera and ostracods shell structures the aim of the study is to assess the heavy metal contamination level and mobility by identifying the trapping phases the study includes analyses by icp aes and icp ms of respectively major si al mg ca fe mn ti na k p and trace elements sr ba v ni co cr zn cu as pb cd in sediments and suspended matter heavy metals enrichment factors calculations and sequential extractions results show that sediments contain zn cu pb v cr co as ni with minimum and maximum concentrations respectively of 4 1190 g g 4 466 g g 11 297 g g 11 194 g g 9 139 g g 1 120 g g 4 76 g g 2 62 g g high concentrations in zn are also present in suspended matter the enrichment factors show contamination in zn pb and as firstly induced by the mining industry and secondly by unauthorized dumps and untreated wastewaters cr and ni are bound to clays whereas v co cu and zn are related to oxides thus the risk in metal mobility is for the latter elements and lies in the oxidation reduction changing conditions of sediments

nd and sr isotope compositions in modern and fossil bones proxies for vertebrate provenance and taphonomy abstract rare earth elements ree while not essential for the physiologic functions of animals are ingested and incorporated in ppb concentrations in bones and teeth nd isotope compositions of modern bones of animals from isotopically distinct habitats demonstrate that the 143 nd 144 nd of the apatite can be used as a fingerprint for bedrock geology or ambient water mass this potentially allows the provenance and migration of extant vertebrates to be traced similar to the use of sr isotopes although ree may be enriched by up to 5 orders of magnitude during diagenesis and recrystallization of bone apatite in vivo 143 nd 144 nd may be preserved in the inner cortex of fossil bones or enamel however tracking the provenance of ancient or extinct vertebrates is possible only for well preserved archeological and paleontological skeletal remains with in vivo like nd contents at the ppb level intra bone and tooth ree analysis can be used to screen for appropriate areas large intra bone nd concentration gradients of 10 1 10 3 are often measured nd concentrations in the inner bone cortex increase over timescales of millions of years while bone rims may be enriched over millenial timescales nevertheless e nd values are often similar within one e nd unit within a single bone larger intra bone differences in specimens may either reflect a partial preservation of in vivo values or changing e nd values of the diagenetic fluid during fossilization however most fossil specimens and the outer rims of bones will record taphonomic 143 nd 144 nd incorporated post mortem during diagenesis unlike ree patterns 143 nd 144 nd are not biased by fractionation processes during ree uptake into the apatite crystal lattice hence the e nd value is an important tracer for taphonomy and reworking bones and teeth from autochthonous fossil assemblages have small variations of 1 e nd unit only in contrast fossil bones and teeth from over 20 different marine and terrestrial fossil sites have a total range of e nd values from 13 0 to 4 9 n 80 often matching the composition of the embedding sediment this implies that the surrounding sediment is the source of nd in the fossil bones and that the specimens of this study seem not to have been reworked differences in e nd values between skeletal remains and embedding sediment may either indicate reworking of fossils and or a ree uptake from a diagenetic fluid with non sediment derived e nd values the latter often applies to fossil shark teeth which may preserve paleo seawater values complementary to e nd values 87 sr 86 sr can help to further constrain the fossil provenance and reworking

bubble coalescence in basaltic lava its impact on the evolution of bubble populations morphological properties bubble number density porosity mean radius specific surface area of vesicular rocks provide quantitative information on the rates of bubble nucleation growth and coalescence in magmas when measured as a function of time such data are useful in constraining the timing and style of gas release during volcanic eruptions volcanic rocks commonly show strong zonation with respect to bubble size and porosity indicating a variation in the amount of bubble growth and coalescence preserved within a single sample morphological properties and bubble size distributions bsd s were measured in a suite of zoned alkali basalts using image analysis and the data were compared to theoretical predictions our data indicate that at porosities greater than 35 extensive coalescence occurred during the growth of bubbles with restricted nucleation at lower porosities vesiculation is dominated by nucleation and diffusion with no coalescence the interiors of many of our samples have undergone 4 7 binary coalescence events after eruption in a time of around 15 min the ostwald ripening effect has not significantly modified the bsd s

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

electrical conductivity and pore space topology of merapi lavas implications for the degassing of porphyritic andesite magmas pore space topology is studied in recent compact angular blocks and scoria fragments om block and ash flow deposits of merapi volcano indonesia connected porosity and electrical conductivity of cored clay4 ee samples are measured in the laboratory at varying fluid salini ty the electrical brmation fiactor tortuosity and cementation index are derived and the pore space topology isbund to be porosity dependent the electrical flow pattern is controlled by crack like paths in compact angular block and by vesicles geometry in more porous scoria agments because merapi lavas are highly viscous and crystal rich we infer that the development of pore connectedness and vesicle coalescence is promoted by shear strain along with ascent rate considerations we conclude that degassing of merapi magma occurs mostly in the conduit during ascent

predictive modelling of prospectivity for pb zn deposits in the lawn hill region queensland australia a combination of geodynamic modelling mineral potential mapping and mineral deposit studies are commonly used to explore for mineral deposits this paper focuses on the mineral potential aspect exploring the interrelationship between a knowledge driven approach which uses subjective evidence based on expert knowledge and a data driven model based on bayesian probabilistic reasoning the limitations and strengths of these approaches provide an example of how blending human interpretation with computational models can be an effective way to aid exploration and ore genesis interpretation the study is focused on the lawn hill platform mount isa inlier situated in northwestern queensland australia the models are used to predict the mineral potential in the area focussing on sedex sedimentary exhalative deposits and vs vein style pb zn mineralisation the lawn hill region shows good mineral potential close to the termite range fault within areas marginal to known prospects and vein lode hosted deposits however there are lower favourability sites suggesting significant potential in the kamarga dome integration of the knowledge and data driven models is considered a potential way to more reliably assess the favourability of locating a century type system the use of this combined technique suggests that the highest favourability of locating a shale hosted mineralisation similar to century is close to this deposit along the termite range fault zone one particularly prospective site has been identified north of the edith cluster

interpretation of long offset transient electromagnetic data from mount merapi indonesia using a three dimensional optimization approach in the years 1998 2000 and 2001 long offset transientelectromagnetic lotem surveys were carried out at the active volcanomerapi in central java the measurements investigated the conductivitystructure of the volcanic edifice our area of interest which is belowthe summit and the upper flanks was investigated using horizontal andvertical magnetic field time derivative data from seventransmitter receiver setups because of topography and athree dimensional 3 d underground structure a 3 d interpretation isused the method optimizes few parameters of a 3 d model by a stableleast squares joint inversion of the data providing sufficientresolution capability reasonable data fits are achieved with anonhorizontally layered model featuring a very conductive basement belowdepths of 1 5 km while hydrothermal alteration is also considered wetentatively explain the high conductivities by aqueous solutions withrelatively high salt contents a large magma body or a small superficialreservoir below merapi s central volcanic complex as discussed by otherauthors cannot be resolved by the lotem data

diagenesis in prehistoric caves the use of minerals that form in situ to assess the completeness of the archaeological record an interpretation of the archaeological record in particular that of a prehistoric cave site is complicated by the diversity of depositional and post depositional processes that affect the material deposited here we propose to use the authigenic minerals that form in situ within the cave sediments to reconstruct the ancient chemical environments in the sediments this can be done by experimentally determining the conditions under which each of the authigenic minerals are stable although this information is not available to date for minerals formed in a prehistoric cave we present calculated stability field data for the relevant minerals the results clearly demonstrate the feasibility of this approach this information particularly if based on measurements of real authigenic cave minerals will facilitate an assessment of the completeness of the cave archaeological record this is particularly important for determining whether or not the distributions of archaeologically important materials such as bones teeth plant phytoliths charcoal and ash reflect their original burial distributions or were altered as a result of secondary diagenetic processes

comparative diagenesis and rare earth element variation in miocene invertebrate and vertebrate fossils from panama abstractthe incorporation of rare earth elements rees into the mineral lattices of skeletonized fossils has been used particularly in vertebrates to understand diagenesis and other postmortem paleoenvironmental parameters little is known about similar processes in invertebrates invertebrate and vertebrate fossils were analyzed for ree concentrations and patterns from five miocene formations in central panama 20 6 m yr ago these formations culebra cucaracha gatun chucunaque and chagres contain sediments interpreted to range from freshwater to shallow marine environments depth of 300 m we also compared different compositional types of fossils including hydroxylapatite bone and aragonite otoliths in vertebrates and calcite and aragonite in invertebrates rees from modern invertebrates indicate that as previously reported for vertebrates invertebrates do not incorporate significant amounts of rees into their mineral lattices during life therefore uptake must primarily occur during diagenesis comparisons of reen concentrations ree concentrations normalized to post archean australian shale of the fossils from panama indicate differences in diagenesis within our largest sample from the gatun formation there are significance differences in reen concentrations and patterns within different compositional types for example shark teeth have the highest reen concentrations and otoliths the lowest with these differences likely a result of physical chemical and mineralogical factors calcitic and aragonitic fossils from the gatun formation show reen patterns indicating differential uptake of individual elements during diagenesis the cerium anomaly previously used to indicate relative paleobathymetry did not discriminate water depth in the marine formations comparative analysis of rees in vertebrates and invertebrates provides a powerful tool to understand diagenetic processes as demonstrated in the five formations and different compositional types studied from the miocene of panama

sulfur enrichment of humic substances in a delaware salt marsh sediment core abstract humic sulfur operationally defined as the sulfur extracted with humic substances in 0 l n naoh solution comprises up to 51 of the total sulfur inventory in a sediment core taken from a delaware spartina alterniflora marsh pyrite sulfur is the next largest fraction except at the near surface sediments where zerovalent sulfur concentrations are significant x ray photoelectron spectroscopy indicates that the humic sulfur consists of sulfoxides or sulfones and in a more reduced state organic sulfides and or organic polysulfides a subsurface decrease in the humic acid c s atomic ratio to 56 2 suggests that the upper 4 cm of marsh sediment is the locus for humic sulfur formation s alterniflora detritus and microbial biomass cannot fully account for observed sulfur enrichment of humic c s atomic ratios therefore the enrichment of humic substances by sulfur is probably via reaction of reduced sulfur compounds with organic matter a humic sulfur formation rate of 10 6 mol s cm 3 a 1 is calculated for the surface sediments and leads to an areal production of 18 mol s cm 2 a 1 of humic sulfur humic sulfur formation and preservation is enhanced by the limited availability of iron for the rapid precipitation of iron sulfide minerals and the apparent resistance of organic sulfur compounds towards reoxidation to sulfate especially in the upper 9 cm of marsh sediment where inorganic sulfur compounds are rapidly oxidized

molecular preservation and crystallographic alterations in a weathering sequence of wildebeest bones abstract the changes that occur in bone after the death of an animal are important because they control whether the bone becomes a fossil and what information is retained concerning the original biology of the animal taphonomic study of two 10 year longitudinal samples of wildebeest bones subjected to natural weathering in amboseli park kenya provides evidence for progressive change in both the organic and inorganic components of mammalian bone these changes correspond to weathering stages described on macroscopic structural features the bone samples were subjected to well established techniques of protein extraction from mineralized tissue protein identification by gel electrophoresis and reactivity to antibodies of noncollagenous proteins as well as x ray defractometry of the mineral component both adult and juvenile bones show progressive increase in hydroxyapatite crystal size and increased protein degradation over the 10 year period noncollagenous proteins persist at their original molecular weight in diminished amounts relative to modern controls in the study area 10 years or less of natural surface weathering altered the extractability of collagen indicating peptide and crosslinking cleavage in this protein increased hydroxyapatite crystal size may reflect a tendency of crystals to enlarge in situ once the organic matrix begins to breakdown without the addition of external minerals

rare earth element systematics of fossil bone revealed by la icpms analysis intra bone rare earth element ree fractionation trends were studied by la icpms analysis to put constraints on 1 the mechanisms controlling ree fractionation within fossil bones 2 the relative timing of ree uptake in various parts of fossil bone and 3 the origin of ree in fossil bones we have evaluated ree bone profiles across 54 fossil bones from a broad range of well characterised taphonomic settings ranging in age from triassic to early medieval ree patterns and concentration gradients are highly variable and intra bone fractionation trends in la yb n vs la sm n space of few specimens cover almost the entire range previously observed for bulk samples intra bone variability of ce anomalies as well as variable y ho and la la n is also observed sometimes diagenetic fluids with fractionated hree enriched compositions have entered the bone from the marrow cavity producing secondary ree uptake profiles theoretical intra bone fractionation trends modelled using lattice strain theory concur with most ree data but some trends cannot be modelled using realistic boundary conditions this fact as well as the occurence of positive and negative ce anomalies within the same fossil sample hint towards changing ree compositions of diagenetic fluids over the timescales of ree uptake because apparent ce anomalies frequently evolve over bone profiles and ce anomalies can be inherited from previous fractionation events ce anomalies are a highly ambiguous tracer for constraining ambient redox conditions in general bioapatite ree signatures may not always reliably reflect ambient taphonomic or redox conditions and diagenetic fluid compositions therefore ree patterns and ce anomalies of fossil bones must be interpreted cautiously as they vary spatially within skeletal remains and are affected by intra bone fractionation processes as well as changing compositions of the diagenetic fluid

early diagenesis of cadmium and cobalt in sediments of the laurentian trough abstract the depth distributions of hydroxylamine acetic acid extractable co and cd were determined in box cores from a series of stations along the 1200 km length of the laurentian trough these were compared with the concentrations of total co and cd and the distributions of extractable mn and fe in the cores as well as with the total cd concentrations in sedimenting particles collected with a sediment trap the results indicate a strongly contrasting behaviour of the two elements during early diagenesis consistent with their respective chemistries and particle associations cobalt occurs mainly in a non reactive form and is buried with the accumulating sediments a mobile component of co is associated with mn and fehydroxides and like these compounds follows a redox sensitive pattern of dissolution in the reducing zone of the sediment vertical migration enrichment by precipitation in the oxidized surface layer and redistribution along the bottom in paniculate form paniculate cd arrives at the sediment surface bound to biogenic material is rapidly solubilized during aerobic degradation of the organic matter and migrates vertically both into the reducing zone of the sediments where it precipitates and back into the water column where it may be recycled through biological processes in an estuary co will be concentrated in the oxidized layer of the sediments and tend to migrate landward while cd will be most abundant in sediments underlying regions where plankton production is high relative to dilution by terrigenous particles

chemical and mineralogical characterisation of weathered historical bricks from the venice lagoonal environment surficial and bulk samples of historical bricks of different age from xii to xviii centuries recovered from a campaign of archaeological excavations recently carried out at the site of a medieval monastery in the s giacomo in paludo island in thevenice lagoon have been characterised by ft ir tga dtg and dta xrd sem eds the samples belong to a particular brick type commonly used in the venice region the altinella brick the bulk relative abundance of primary i e calcite and dolomite and secondary firing minerals i e diopside and wollastonite in the bricks coupled with their relative geometrical dimensions allows placing the samples in a chronological sequence according to known historical changes in brickmaking firing temperatures and practices most of the bricks were used as paving material and have been exposed to the action of seawater salts chlorides and sulphates due to periodical submersion following high tide episodes salt laden gypsum halite mirabilite surficial patinas are indeed present but salt weathering does not appear to have affected the overall structural soundness of the bricks in this now abandoned island as it is the case with brickwork located in other more populated and polluted areas in venice and its lagoon

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

nuees ardentes of 22 november 1994 at merapi volcano java indonesia nuees ardentes associated with dome collapse on 22 november 1994 at merapi volcano traveled to the south southwest as far as 6 5 km and collectively accumulated roughly 2 5 3 million cubic meters of deposits the damaged area comprises 9 5 km2 and is covered by two nuee ardente facies a conventional merapi type valley fill block and ash flow facies and a pyroclastic surge facies the proximal deposits reflect the accumulation of dozens of nuees ardentes with many subsidiary flow units the distal deposits are more simply organized as only a few individual events reached to distances 3 5 km the stratigraphic relationships north of turgo hill indicate that the surge deposits are a facies of particularly mobile nuees ardentes that also deposited channeled block and ash flow facies they further suggest that the surge facies beyond the channel margins correlate laterally with a finer grained sublayer locally developed at the base of the block and ash flow facies eyewitness reports suggest that the emplacement of the block and ash flow facies in the distal part of the boyong river may have followed by a short time interval the destruction and deposition of the surge facies at turgo village the stratigraphy is in accord with the eyewitness reports the surge facies was emplaced by a dilute surge current detached from the same dome collapse nuee ardente that as a separate flow unit subsequently emplaced the distal block and ash deposit in the boyong valley the detachment occurred at higher elevations likely at or above the slope break at about 2000 m elevation this flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block and ash flow continued its tortuous southward movement in the boyong channel dome collapse nuee ardente activity formed the bulk of the eruption which was accompanied by virtually no significant vertical summit explosive activity

neogene forests from the appalachians of tennessee usa geochemical evidence from fossil mammal teeth abstract neogene land mammal localities are very rare in the northeastern u s therefore the late miocene early pliocene gray fossil site in eastern tennessee can clarify paleoecological dynamics during a time of dramatic global change in particular the identification of ancient forests and past climate regimes will better our understanding of the environmental context of mammalian evolution during the late cenozoic stable isotope analyses of bulk and serial samples of fossil tooth enamel from all ungulates present at the gray site elucidate paleoecological reconstructions the herbivorous megafauna include taxa of likely north american and eurasian ancestry including the tapir tapirus polkensis rhino teleoceras cf t hicksi camel cf megatylopus sp peccary tayassuidae and proboscidean gomphotheriidae the tapir rhino camel and peccary yield mean stable carbon isotope 13c tooth enamel values of 13 0 13 3 13 8 and 13 1 respectively suggesting forest dwelling browsers this range of 13c values indicates the presence of a c3 dominated ancient local flora because 13c values decline with increasing canopy density the ancient temperate forests from the gray site were moderately dense the lack of significant c4 plant consumption i e tooth enamel 13c values

geochronology of hemphillian blancan aged strata guanajuato mexico and implications for timing of the great american biotic interchange abstract we present new geochronologic magnetostratigraphy fission track and 40ar 39ar radioisotopic dates biostratigraphy data constraining the age of three separate sequences and a composite section from guanajuato mexico those data make this one of the most complete and precisely age calibrated sequences in north america spanning the hemphillian blancan north american land mammal age nalma boundary interval and the data further constrain the timing and pattern of the great american biotic interchange gabi in total 196 samples 77 sites were used to construct the magnetic polarity stratigraphies with eight fission track analyses and four new 40ar 39ar radioisotopic dates the sections sampled are possibly latest miocene to late pliocene in age spanning about 2 7 m yr 5 5 2 7 ma from chrons c3n 4n or c3r to c2an 1n the radioisotopic dates and magnetostratigraphic correlations indicate the hemphillian blancan nalma boundary at guanajuato in central mexico is 4 7 4 8 ma and it pro

slow rates of degradation of osteocalcin green light for fossil bone protein our claim published in this journal for successful immunodetection of the protein osteocalcin in dinosaur bone has been challenged on the grounds that the findings are inconsistent with the kinetics of decomposition here we show that the close association of osteocalcin to the bone mineral vastly enhances its preservation potential relative to the same protein in aqueous solution we conducted heating experiments 75 95 c of modern bone powder and monitored the survival of three different regions of osteocalcin n terminal his 4 hyp 9 c terminal phe 45 val 49 and the mid region pro 15 glu 31 with monoclonal antibodies extrapolation of our data to 10 c ambient burial temperatures indicates that preservation of the carboxylated mid region in fossil bone cannot be excluded on kinetic grounds clearly in situ sequence analysis will be the only method by which the preservation of fossil macromolecules will be unequivocally established nevertheless our findings demonstrate the importance of mineral association to protein survival as was borne out by an investigation of holocene ca 6 ka bones only in those samples with little recrystallization was the carboxylated mid region well preserved these results imply that the future success of ancient biomolecule research largely depends on our understanding the interaction between these materials and their environment throughout diagenesis

transition from dome forming to plinian eruptive styles controlled by h2o and cl degassing the transition from a plinian pumice to an effusive dome forming eruptive style is frequently observed in volcanic systems and is generally attributed to the progressive loss of volatiles from magma stored in a superficial reservoir this explosive effusive transition has been explained by the evolution from a closed to an open system of degassing1 2 3 4 but in this context an eruption at mt pelee martinique french west indies dated at 650 years ago which exhibited a rarely observed5 6 succession from dome forming to plinian activity in a short interval of time7 is at odds with such an explanation in this eruption near surface explosions of the dome produced two peleean turbulent pyroclastic flows whose deposits are similar to those of the effusive 1902 eruption and then plinian activity produced pumice fallouts and flows the reconstruction of the degassing paths of both eruptive regimes using the densities and the h2o and cl contents of the clasts shows that the interaction of rising magma with hydrothermal fluids at shallow depth may play a critical role in determining eruptive style

protracted diagenetic alteration of ree contents in fossil bioapatites direct evidence from lu hf isotope systematics abstract fossil bones and teeth are potentially important repository for geochemical proxy data and a target for radiometric dating the concentration of many trace elements in bones and teeth increases by orders of magnitude after death and it is this diagenetic incorporation that forms the basis for several areas of geochemical study the use of bones and teeth in this context relies on two assumptions first that target metal ions are incorporated rapidly after death reflecting a known environmental signal and second that after early incorporation the bone or tooth remains as an essentially closed system resistant to later diagenetic change a wide literature has developed exploring these assumptions but relatively little direct evidence has been used to assess the long term diagenetic stability of trace elements within bones and teeth in this study we use the lu hf isotope system to show that bones and teeth of cretaceous and triassic age from both terrestrial and marine settings experience continued long term diagenetic change most likely through gradual addition of trace elements modelling suggests that diagenetic addition after initial recrystallisation may account for 50 of the total ree content in the sampled bones the extent depending on initial uptake conditions tooth enamel and enameloid may be more resistant to late diagenetic changes but dentine is probably altered to the same extent as bone these results have significant implications for the use of bones and teeth as hosts of chronological palaeoceanographic palaeoenvironmental and taphonomic information particularly in mesozoic and palaeozoic contexts

dinosaur bones fossils or pseudomorphs the pitfalls of physiology reconstruction from apatitic fossils abstract a prerequisite to any attempt to reconstruct thermophysiology of ancient animals through analysis of stable isotopes of oxygen is the assumption that apatitic fossils are isotopically unaltered parts of their original skeletons we suggest that sufficient evidence is available to seriously question this assumption because living bones contain about 1 3 by weight of organic matrix mass balance considerations show that at least half of an apatitic fossil must be new material added post mortem furthermore living apatitic skeletons contain almost no rare earth elements and uranium whereas apatitic fossils bear high concentrations of these elements additionally we found that while in living fish correlation between 18o of oxygen in the phosphate and that in the carbonate of apatite is poor these two values are linearly correlated in fossil fish this suggests diagenetic recrystallization has taken place perfect preservation of micro textures such as haversian canals does not prove the pristine condition of a fossil some of the most beautifully preserved fossils are highly silicified most apatitic fossils probably are pseudomorphs replacing original skeletal elements whereas distribution of stable isotopes of oxygen in fossils might provide information about their burial environment it could be misleading in attempts to interpret the organisms physiology this cautionary note is supported by the similarity of 18op in bones of coexisting fossil fish dinosaurs and various other reptiles at different latitudes the overlap of predicted 18op values in fish and mammals living in contact with the same environmental water also weakens the hope that ectotherms can be distinguished from endotherms by the isotopic composition of oxygen in their bones and teeth

patterns of chemical change during bone fossilization the uptake of elements by bone during fossilization is a well recognized phenomenon but the nature of and the factors leading to chemical heterogeneity in fossil bone are only just starting to be elucidated indeed in the recent past the assumption that fossil bone is chemically homogeneous has been commonly used in several investigations including those of bone dating and dietary studies in an attempt to understand the processes of element uptake we have investigated some chemical heterogeneities in a fossil bone and have assessed the potential use of bone composition as an indicator of the trace element contents of associated groundwater our study extends other work1 2 by giving the first analysis of rare earth element ree distribution in a fossil bone and by showing that information on the redox state and ree abundance pattern of the groundwater can be obtained the results contribute to the interpretation of bone analyses in studies on provenance and age determination as well as in the diet and health of past populations

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

mass budget partitioning during explosive eruptions insights from the 2006 paroxysm of tungurahua volcano ecuador how and how much the mass of juvenile magma is split between vent derived tephra pdc deposits and lavas i e mass partition is related to eruption dynamics and style estimating such mass partitioning budgets may reveal important for hazard evaluation purposes we calculated the volume of each product emplaced during the august 2006 paroxysmal eruption of tungurahua volcano ecuador and converted it into masses using high resolution grainsize componentry and density data this dataset is one of the first complete descriptions of mass partitioning associated with a vei 3 andesitic event the scoria fall deposit near vent agglutinate and lava flow include 28 16 and 12 wt of the erupted juvenile mass respectively much 44 wt of the juvenile material fed pyroclastic density currents i e dense flows dilute surges and co pdc plumes highlighting that tephra fall deposits do not depict adequately the size and fragmentation processes of moderate pdc forming event the main parameters controlling the mass partitioning are the type of magmatic fragmentation conditions of magma ascent and crater area topography comparisons of our dataset with other pdc forming eruptions of different style and magma composition suggest that moderate andesitic eruptions are more prone to produce pdcs in proportions than any other eruption type this finding may be explained by the relatively low magmatic fragmentation efficiency of moderate andesitic eruptions these mass partitioning data reveal important trends that may be critical for hazard assessment notably at frequently active andesitic edifices this article is protected by copyright all rights reserved

compaction and gas loss in welded pyroclastic deposits as revealed by porosity permeability and electrical conductivity measurements of the shevlin park tuff pyroclastic flows produced by large volcanic eruptions commonly densify after emplacement processes of gas escape compaction and welding in pyroclastic flow deposits are controlled by the physical and thermal properties of constituent material through measurements of matrix porosity permeability and electrical conductivity we provide a framework for understanding the evolution of pore structure during these processes using data from the shevlin park tuff in central oregon united states and from the literature we find that over a porosity range of 0 70 matrix permeability varies by almost 10 orders of magnitude from 10 20 to 10 11 m 2 with over three orders of magnitude variation at any given porosity part of the variation at a given porosity is due to permeability anisotropy where oriented core samples indicate higher permeabilities parallel to foliation horizontally than perpendicular to foliation vertically this suggests that pore space is flattened during compaction creating anisotropic crack like networks a geometry that is supported by electrical conductivity measurements we find that the power law equation k 1 1 3 10 21 5 2 provides the best approximation of dominant horizontal gas loss where k 1 permeability and porosity application of kozeny carman fluid flow approximations suggests that permeability in the shevlin park tuff is controlled by crack or disk like pore apertures with minimum widths of 0 3 and 7 5 m we find that matrix permeability limits compaction over short times but deformation is then controlled by competition among cooling compaction water resorption and permeable gas escape these competing processes control the potential for development of overpressure and secondary explosions and the degree of welding in the deposit processes that are applicable to viscous densification of volcanic deposits in general further the general relationships among porosity permeability and pore geometry are relevant for flow of any fluid through an ignimbritic host

geochemical study of vertebrate fossils from the upper cretaceous santonian csehbanya formation hungary evidence for a freshwater habitat of mosasaurs and pycnodont fish abstract the diverse vertebrate remains from the upper cretaceous freshwater settings at iharkut hungary contain two fossil groups pycnodontiformes fish and mosasauridae that are almost exclusively known from marine palaeo environments hence their appearance in alluvial sediments is very unusual trace element and isotope compositions of the remains have been analyzed to investigate the taphonomy and the ecological differences among the different fossil groups present at iharkut all examined fossils have undergone post depositional diagenetic alteration which resulted in high concentrations of ree u and fe together with almost complete homogenization of 18oco3 values similar ree patterns in different fossils suggest a common origin for all remains hence the discovered species most likely lived in the same local ecosystem despite partial diagenetic overprinting the 18opo4 values of the fossils indicate sufficient taxon specific isotopic diversity to permit some broad conclusions on the palaeo environment of the fossils in particular it is apparent that the isotopic composition of the pycnodontiformes fish and mosasauridae remains is most compatible with a freshwater palaeo habitat and incompatible with a marine palaeo environment in addition the sr concentration and isotope data indicate that the pycnodontiformes and mosasauridae likely lived predominantly in a freshwater environment and were not simply occasional visitors to the iharkut river ecosystem regarding other fossil groups high 18opo4 values of alligatoroidea and iharkutosuchus teeth suggest that these small crocodile species might have inhabited swamps and ponds where the water was relatively rich in 18o due to evaporation

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

merapi volcano central java indonesia a case study of radionuclide behavior in volcanic gases and its implications for magma dynamics at andesitic volcanoes for more than 20 years volcanic gases have been regularly collected at merapi volcano indonesia and have been subsequently analyzed for their 210pb 210bi and 210po activities and so2 contents these new results show the high volatility of the three radionuclides in andesitic gases although their emanation coefficients 0 94 3 5 and 53 for 210pb 210bi and 210po respectively are significantly lower than those observed at basaltic volcanoes this emphasizes the major role of magma temperature on the degassing of these metals which are mainly transported in volcanic gases as pb chloride compounds and as bi and po metallic species radioactive disequilibria between 210pb 210bi and 210po in the gas phase are characteristic of degassing processes and gas paths within the edifice gases released at both gendol and woro fumarolic fields are of magmatic origin but their radionuclide content is strongly altered by secondary processes chemical reactions with surrounding brines and deposition of sublimates in the ground high temperature gases collected in the summit gas plume are of pure primary magmatic origin and are likely directly tapped in the degassing reservoir gases arising from the growing domes are strongly depleted in the most volatile isotopes and gas species this suggests that magma mostly degasses at depth in open system explaining why the volcano usually undergoes no explosive eruptions the gas flux at merapi is sustained by a deep magma supply which is twice the extrusion rate of lava unerupted degassed magma thus progressively accumulates beneath the summit yielding an overpressure which can trigger dome collapse without precursor

patterns of diagenesis in bone i the effects of site environments abstract we have measured a suite of diagenetic parameters for several populations of archaeological bones buried in a number of northwest european sites since the last ice age these are the structural damage due to microbes changes in bone micro and macro porosity protein content a measure of the crystallinity of hydroxyapatite as reflected in the phosphate infra red spectrum peak splitting and a measure of the carbonate content as given by the ratio of carbonate to phosphate infra red absorption peaks the results provide a database that clearly characterises the patterns which are often site dependent of diagenetic change in buried bone our main conclusions are that individual site hydrology appears to have a strong influence on the outcome of bone preservation and that porosity is the most effective single diagenetic parameter which both determines and reflects the preservation of bone in the burial environment

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

a geochemical method to trace the taphonomic history of reworked bones in sedimentary settings rare earth element ree signatures can be used to identify the original mode of deposition of fossil bones and teeth that have been reworked this new technique may resolve the notoriously difficult problem of assessing the amount of transport or reworking undergone by fossil bones and teeth on the basis of physical parameters such as degree of abrasion different ree signals characterize different pore water environments bones and teeth composed of apatite incorporate rees rapidly during early diagenesis and the ree signature in the bone is controlled by that of the surrounding pore waters reworked bones and teeth may show ree traces suggesting early diagenetic pore water conditions different from those indicated by in situ sedimentary or geochemical evidence this situation is demonstrated in a case study from the rhaetian latest triassic of southwest england where different bone beds are compared in one case the original environmental setting of reworked bone is traced by matching ree traces with contemporaneous unreworked bone assemblages in neighboring areas

measurements and relationships of diagenetic alteration of bone from three archaeological sites four diagenetic parameters have been chosen to represent the state of diagenesis of bone buried on archaeological sites they are histological preservation protein content crystallinity and porosity how these parameters are measured is described and results from populations of bones from three different sites are presented the results show the extent and variation in the degree of change both within a site and between sites in particular the correlations between diagenetic parameters are examined which give clues about the processes which cause alteration the value of porosity determinations both at the intercrystalline level and at coarser levels in revealing the degree of diagenetic change in bone and in underlying the dynamics of the interaction between buried bone and the surrounding water is stressed the data also indicate but are too restricted to prove the following microbiological attack is generally complete within less than 500 years substantial levels of protein may remain in bone after maximal micromorphological alteration loss of protein appears to be independent of other diagenetic change the correlated lose of microporosity with increase of crystallinity suggests these changes may arise from the dissolution perhaps with subsequent recrystallization of the smallest hydroxyapatite crystallites

magma eruption rates of merapi volcano central java indonesia during one century 1890 1992 the magma eruption rates of merapi volcano form 1890 to 1992 are re examined chronologically for this volcano movements of extruded lavas and domes as well as their extrusions are important because they control the modes of the subsequent activities and cause nuees ardentes and lahars the monthly eruption rates varied widely but the cumulative volume of lavas has increased linearly and is expressed as 0 1x106 m3 month the magma production rate of this volcano may have been constant for these 100 years recurrent excessive effusion of lavas is tentatively interpreted by assuming a magma reservoir the averaged eruption rate is small in comparison with other volcanoes such as nyramuragia kilauea and vesuvio however it is remarkable that the activity has been continuous for these 100 years and the total amount of lava discharged during this period reached more than 108 m3 a simple model for the formation of the 1992 lava dome is presented the viscosity of the lavas is probably between 106 and 107 p and the length of the magma conduit is probably less than 10 km

visualizing fossilization using laser ablation inductively coupled plasma mass spectrometry maps of trace elements in late cretaceous bones elemental maps generated by laser ablation inductively coupled plasma mass spectrometry la icp ms provide a previously unavailable high resolution visualization of the complex physicochemical conditions operating within individual bones during the early stages of diagenesis and fossilization a selection of la icp ms maps of bones collected from the late cretaceous of montana united states and madagascar graphically illustrate diverse paths to recrystallization and reveal unique insights into geochemical aspects of taphonomic history some bones show distinct gradients in concentrations of rare earth elements and uranium with highest concentrations at external bone margins others exhibit more intricate patterns of trace element uptake related to bone histology and its control on the flow paths of pore waters patterns of element uptake as revealed by la icp ms maps can be used to guide sampling strategies and call into question previous studies that hinge upon localized bulk samples of fossilized bone tissue la icp ms maps also allow for comparison of recrystallization rates among fossil bones and afford a novel approach to identifying bones or regions of bones potentially suitable for extracting intact biogeochemical signals

rare earth element composition of paleogene vertebrate fossils from toadstool geologic park nebraska usa fossil bones and teeth from terrestrial environments encode unique rare earth and trace element ree and te signatures as a function of redox conditions ph concentrations of complexing ligands and water colloid interactions this signature is set early in the fossilization process and serves as a paleoenvironmental and paleoclimatic proxy these signatures can also be used to interpret temporal and spatial averaging within vertebrate accumulations and can help relocate displaced fossil bones back into stratigraphic context rare earth elements in vertebrate fossils from upper eocene and oligocene strata of toadstool geologic park northwestern nebraska record mixing and evolution of paleogene vadose or groundwaters and variations in paleoenvironments ree signatures indicate that hree enriched alkaline groundwater reacted with lree and mree enriched sediments to produce 3 component mixtures ree signatures become increasingly lree and mree enriched toward the top of the studied section as the paleoenvironment became cooler and drier suggesting that ree signatures may be climate proxies time series analysis suggests that ree ratios are influenced by cycles of ca 1050 800 570 440 and 225 ka similar to some previously determined milankovitch astronomical and climate periodicities

effect of paleosol formation on rare earth element signatures in fossil bone the rare earth element ree content of fossil bones was analyzed and compared with the degree of ancient pedogenic development and depositional environments from several locations in the orellan scenic member of the oligocene brule formation in badlands national park south dakota paleosols ranged from weakly developed entisols to more strongly developed inceptisols all typical of fluvial environments and possible paleocatena variation paleosols were alkaline and well drained sediments with sparse soil features from an oxbow lake system suggest that conditions were too waterlogged and sedimentation rates too rapid for significant pedogenesis the variance of ree signatures in fossil bones from the paleosol sites was significantly greater than that of fossils from minimally altered sediments of the former oxbow lake positive ce anomalies were associated with low u concentrations and indicate paleoredox conditions greater degrees of pedogenesis regardless of the horizon in which the bone was found systematically correlated with increased heavy ree enrichment in fossil bones the fossil bone ree signatures from the different paleosols and depositional environments were significantly different and distinguishable

calibration of mammoth mammuthus dispersal into north america using rare earth elements of plio pleistocene mammals from florida the first appearance of mammoth mammuthus is currently used to define the beginning of the irvingtonian north american land mammal age at about 1 4 ma thereafter mammoth fossils are common and widespread in north america until the end of the pleistocene in contrast to this generally accepted biochronology recent reports have asserted that mammoth occurs in late pliocene ca 2 5 ma alluvium from the santa fe river of northern florida the supposedly contemporaneous late pliocene fossil assemblage from the santa fe river that produced the mammoth specimens actually consists of a mixture of diagnostic blancan late pliocene and late rancholabrean latest pleistocene species fossil bones and teeth of the two mammalian faunas mixed together along the santa fe river have significantly different rare earth element ree signatures the ree signatures of mammoth are indistinguishable from those of rancholabrean mammals yet they are different from those of diagnostic blancan vertebrates from these same temporally mixed faunas of the santa fe river thus no evidence for late pliocene mammoth exists in florida and mammoth fossils remain reliable biochronological indicators for irvingtonian and rancholabrean terrestrial sequences throughout mid and lower latitude north america

on the origin and significance of pyrite spheres in devonian black shales of north america abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts that are typically preserved as flattened circular discs on bedding planes work by the present authors shows that cysts can be preserved as pyrite infill casts that are expressed as sand size whole and geopetal half spheres of pyrite at the bases of thin black shale layers these occur in situ at many stratigraphic levels in the distal prodelta facies of the catskill delta complex of new york as well as in laterally equivalent black shales in tennessee and kentucky reworked pyrite casts usually dominated by whole spheres form lenticular lag accumulations and hydraulic placers together with plant debris and phosphatic particles bone debris conodonts an earlier model for the formation of pyrite spheres in gas bubbles is rejected in favor of formation within uncompressed tasmanites cysts direct observation of cyst cuticle in association with pyrite spheres suggests that localized bacterial sulfate reduction in tasmanites interior voids led to formation of localized pyrite deposition in a manner similar to that described from certain ammonoid chamber settings cyst fill commenced with formation of framboidal pyrite followed by later diagenetic pyrite cementation between framboids these fills show geopetal features and appear to have formed within the redox zone below the sediment water interface although described here from the upper devonian comparable pyrite textures are also known from proterozoic cambrian ordovician and silurian sediments they probably occur throughout the sedimentary record and in mudstone successions they may prove to be an important source of sand size grains in areas far removed from the basin margins as such they may be important for detection of erosive events and strong bottom currents and provide valuable information about the depositional history of mudstone successions

fractionation of rare earth elements within bone mineral a natural cation exchange system the distribution of rare earth elements rees within fossil bones is controlled by their partition coefficients between apatite and pore waters and the rate of diffusion through the bone using simple theoretical models we show that rees are strongly fractionated from one another during diffusive transport and adsorption fractionation occurs due to the relative ease of substituting ree ions of differing ionic radius into the ca sites in the apatite lattice and the degree of fractionation is dependent on the rate of diffusion of ions within bone and therefore the rate of recrystallisation variations in bone thickness recrystallisation rate and potentially pore water composition may all influence the relative distribution of rees and thus ree ratios within bones increases in bone thickness and reductions in either diffusion coefficients or the duration of ree uptake lead to enhanced fractionation of rees in our model simulations interpretations of ree ratios in fossil bones either for palaeoenvironmental or taphonomic applications must consider how fractionation will influence ree ratios within bones particularly when interpreting spatially resolved analyses within single bones

electromagnetic evidence for an ancient avalanche caldera rim on the south flank of mount merapi indonesia abstract long offset transient electromagnetic lotem data and vibrotem data from the south flank of mount merapi on java island indonesia are interpreted with one dimensional 1d inversions as well as two dimensional 2d forward modelling one dimensional joint inversions of several components of the electromagnetic field with occam s method reduce the number of equivalent models which were derived from inversions of single components and fit the data to a similar misfit the 1d results together with results from other geophysical measurements serve as the basic model for further 2d forward modelling the final model depicts a layering that follows the topography of the strato volcano in the depth range of 500 m to 1000 m the resistivity of the layers decreases rapidly downwards into a good conductor with resistivities below 10 m the deepest layer has a resistivity of 0 4 m which is quantitatively explained with a combination of saline fluids and hydrothermally altered minerals furthermore the final model supports a hypothesis from the interpretation of central loop tem transient electromagnetic data that there is a fault structure below the southern flank approximately 7 3 km south of the summit to the north of the fault the top of the good conductor is lowered from a depth of 500 m to 1000 m we propose that the fault structure coincides with an ancient avalanche caldera rim

variability of trace element uptake in marine reptile bones from three triassic sites s poland influence of diagenetic processes on the host rock and significance of the applied methodology abstract diagenetic alternation of apatite building vertebrate bioclasts is a complex process it is influenced by numerous factors but the impact of diagenetic processes affecting the host rock is commonly underestimated the present study aims at identifying the causes of different concentration levels and distribution patterns of ree and at examining the significance of the material chosen for normalisation we measured ree and other trace element concentrations in three bone assemblages of triassic marine reptiles using la icp ms and in the host rocks using icp ms two groups of hard parts reveal clearly different trace element contents and distribution patterns the remains from gogolin show a distinct mreen enrichment which must have been caused by replacement involving numerous substitutions that was possible due to a relatively high porosity of the host rocks and the presence of pore water the mreen enrichment and low concentrations of mg and sr combined with a relatively high content of u in these bones indicate solutions derived from meteoric water as the source of the incorporated ions the reductive dissolution of fe oxyhydroxides that are abundant in the host rock matrix and that likely were an important source of ree may have influenced and controlled the ree uptake the significant hreen enrichment over lreen as revealed in the rust coloured bones from raciborowice gorne is likely connected with local acidification of the pore water resulting from aqueous oxidation of pyrite infilling the pore spaces in the bones the material selected for normalisation of the chemical composition of apatite can have a significant impact on values of the normalised data used further for interpretations particularly when vertebrate bioclasts from carbonate host rocks are involved the carbonate rocks have element ratios that differ from those characterising the commonly used paas and nasc normalisation materials in particular ce anomaly values can distinctly vary depending on the applied normalisation procedure vertebrate hard parts that definitely spent more time in a host rock than in an animal body must be rigidly handled as a constituent of a specific rock never as a separate item

an overview of the seismicity of merapi volcano java indonesia 1983 1994 abstract from 1982 to 1995 merapi volcano java indonesia experienced two main eruptive cycles from 1984 to 1986 and from 1992 to 1994 each cycle had a duration slightly larger than 2 years four major eruptive events occurred in 1984 1986 1992 and 1994 these eruptions were monitored by a telemetered seismic network we present an overview of the seismicity observed between 1983 and 1995 from seismological observations several types of characteristic events are recognised volcanotectonic earthquakes are standard microearthquakes either shallow an aseismic zone is situated between two seismic zones at a depth between 1 5 and 2 5 km below the summit we postulate that it is a small shallow magma reservoir where magma injected from below can be stored temporarily we try to relate seismic observations during both eruptive cycles to the initial injection of deep magma to the superficial magma system the first eruption in each case seems to involve magma enriched in gas that extrudes the content of the conduit and explodes the old dome a regular outflow of magma follows the initial explosion and gradually a dome is building up then it stops and a period of repose is observed later a second episode of dome growth occurs the height of the dome reaches a maximum corresponding to a state of lithostatic equilibrium the time delay of more than 2 years between the beginning and the end of a cycle may result from crystallisation in a volatile rich magma and from the building up of pressure in the superficial magma pocket some important events like the collapse of the dome on 22 november 1994 are not preceded by any seismic precursor when it reaches a large volume the dome is not stable and is likely to collapse by gravity for instance after the sudden influx of matter or gas or after a heavy rain on merapi tremors are observed but do not always precede a dangerous event

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

lithostratigraphy tephrochronology and rare earth element geochemistry of fossils at the classical pleistocene fossil lake area south central oregon abstract one of the most famous fossiliferous pleistocene sites in the pacific northwest is fossil lake oregon until recently fossil collections from the area were not stratigraphically controlled owing to the lack of a detailed stratigraphic and chronologic framework our field studies reveal at least nine exposed thin rhythmic fining upward depositional packages most separated by disconformities analysis of interbedded tephras reveals that the rye patch dam 646 ka dibekulewe 610 ka tulelake t64 95 ka marble bluff 47 ka and trego hot springs 23 2 ka tephra layers are present in the section indicating deposition from more than 646 ka to less than 23 ka which includes both the late irvingtonian and rancholabrean north american land mammal ages a much longer time span than previously believed bones analyzed from eight of the defined units have distinctly different rare earth element ree signatures fossils obtain ree during early diagenesis and signatures are probably closely

vesicle connectivity in pyroclasts and implications for the fluidisation of fountain collapse pyroclastic flows montserrat west indies abstract pyroclastic flows are noted for their highly mobile behaviour being able to flow on slopes as low as a few degrees and this has been attributed to fluidisation or partial fluidisation by escaping gases the three types of pyroclastic flows generated during the eruption of soufriere hills volcano on montserrat dome collapse fountain collapse and surge derived differ in their apparent mobility suggesting different degrees of fluidisation and friction reduction in the flowing granular materials several possible sources of fluidising gas operate in pyroclastic flows the purpose of this paper is to assess the feasibility of one mechanism the release during flow of pressurised gases trapped in the vesicles of juvenile clasts measurements with a helium pycnometer show that all vesicles in dense lava blocks from dome collapse pyroclastic flows are connected so that the mechanism is probably not viable for such flows on the other hand pumices from fountain collapse pyroclastic flows from soufriere hills and other volcanoes contain up to 10 vol of isolated vesicles this is confirmed by sem imagery which shows that soufriere hills pumices contain two vesicle populations with a bimodal size distribution the large vesicles are mostly interconnected whereas about two thirds of the smaller population

mineralogical and compositional changes in bones exposed on soil surfaces in amboseli national park kenya diagenetic mechanisms and the role of sediment pore fluids abstract bones exposed on tropical savannah grasslands of amboseli national park kenya undergo extensive post mortem alteration within 40 years a combined analytical approach involving tem microscopy trace metal analysis ftir spectroscopy and petrographic analysis has revealed a complex dynamic diagenetic environment operating within exposed bones driven by evaporative transport of soil water from the bone soil interface to the upper exposed surface of the bone this process results in extensive bone soil water interaction and is responsible for increases in the concentrations of trace elements such as ba and la of 100 1000 within 15 years the maximum and mean size of bone crystallites increases with continued exposure this change in mean crystallite length is correlated positively with increases in bone crystallinity which in turn is associated with degradation of the bone protein microbial decomposition is rarely observed in the amboseli bones but where present resulted in severe dissolution reprecipitation of bone mineral many bones showed extensive permineralization of the larger vascular spaces with calcite and barite and to a lesser extent crandallite permineralization of unburied bones may account for 95 reduction in macro micron millimeter scale porosity in the bone within 2 years of death we produce a model for pre burial diagenesis of bone in arid tropical environments that highlights extensive alteration of bone chemistry within 1 40 years post mortem

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

reconstruction of caribbean sea surface temperature and salinity fluctuations in response to the pliocene closure of the central american gateway and radiative forcing using δ44 40ca δ18o and mg ca ratios the 18o values of planktonic foraminifera increased in the caribbean by about 0 5 relative to the equatorial east pacific values between 4 6 and 4 2 ma as a consequence of the closure of the central american gateway cag this increase in 18o can be interpreted either as an increase in caribbean sea surface mixed layer salinity sss or as a decrease in sea surface temperatures sst this problem represents an ideal situation to apply the recently developed paleotemperature proxy 44 40ca together with mg ca and 18o on the planktic foraminifer globigerinoides sacculifer from odp site 999 although differences in absolute temperature calibration of 44 40ca and mg ca exist the general pattern is similar indicating a sst decrease of about 2 3 c between 4 4 and 4 3 ma followed by an increase in the same order of magnitude between 4 3 and 4 0 ma correcting the 18o record for this temperature change and assuming that changes in global ice volume are negligible the salinity induced planktonic 18o signal decreased by about 0 4 between 4 4 and 4 3 ma and increased by about 0 9 between 4 3 and 4 0 ma in the caribbean the observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the caribbean and the pacific in response to the shoaling of the panamanian seaway possibly accompanied by a southward shift of the intertropical convergence zone itcz between 4 4 and 4 3 ma differences in mg ca and 44 40ca derived temperatures can be reconciled by corrections for secular variations of the marine mg casw and 44 40ca a salinity effect on the mg ca ratio and a constant temperature offset of 2 5 c between both sst proxy calibrations

geochemical characteristics of western ross sea antarctica sediments abstract a geochemical study of bottom sediments from 50 stations in various ross sea sedimentary environments ranging from the coastal strip to the external platform situated off southern victoria land between the david and mariner glaciers has demonstrated the silicate nature of these sediments and significant variations in the major element concentrations the presence and concentrations of the trace elements studied cr ni co v cu pb zn and cd differ from one geographic area to another and within a given basin a statistical analysis of the geochemical variables using the cluster method shows that si is independent of the other elements which group into associations a multivariate statistical analysis based on geochemical granulometric and environmental parameters identifies five distinct sediment groups located in different areas of sedimentation and with peculiar geochemical characteristics group 1 on the external platform which comprises very fine sediments is characterised by the highest contents of mg loi cr ni and v and of cu and zn group 2 from the banks formed by pelitic sands is distinguished on the basis of lower cu and zn and higher cr and si group 3 on the internal platform consisting of sandy sediments comprises high values of na al ca and pb and low values of zn and v group 4 in the coarse coastal sands is enriched in co and ca na k and al group 5 formed by materials with different grain size distribution located south of coulman island is distinguished by a very high content of zn fe ti and na with cr co pb and si being found at lower levels the materials are glacial detrital are derived from the rocky hinterland formations and are reworked by transport and deposition processes depending on the energy level of the marine sedimentary environments given the scarcity of comparison data from the hinterland rocks it is difficult to establish the parent rocks of these glaciomarine sediments on the basis of geochemical data alone only in the case of the sediments south of coulman island can one be certain of a contribution from the mcmurdo volcanics for the external platform sediments the highest contents of si and l o i confirm the input of material from biogenic neoformation

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

cesium 137 metals and organic carbon in the sediments of the james river estuary virginia abstract a wide variety of sedimentary subenvironments are found within a 10 km stretch of james river including a flood dominated channel rocklanding channel and its bank rocklanding shoal a shoal with a water depth of 1 m separating two channels point of shoals an ebb dominated channel burwell bay channel and its bank burwell bay bank and a tributary warwick river the concentrations of cs 137 cu pb zn and organic carbon in the fine grained sediments i e 3 cm year 1 the sedimentation rates in the burwell bay region are two or more times those in the point of shoals and in the rocklanding channel and shoal reflecting the weaker currents in the burwell bay region these sedimentation rates agree well with those obtained independently by measuring changes in the bathymetry of this area between 1873 and 1943 the concentrations of cs 137 cu pb zn and organic carbon in surface sediments vary by a factor of two to three the concentrations are higher in the burwell bay region probably as a result of the higher rates of accumulation of recently formed sediments in these subenvironments the inventories of fine grained sediments and of cs 137 cu pb zn and organic carbon accumulated since 1954 are also up to an order of magnitude higher in the burwell bay region although the concentrations of fine grained sediments in three cores obtained in this region are similar the inventories still vary by a factor of two to three the inventories of cs 137 cu pb zn organic carbon and fine grained sediments correlate well with each other indicating that cs 137 can be a useful tracer for studying the fate of these metals and organic carbon in estuarine environments the inhomogeneity of the concentrations and inventories of the different elements along a 10 km segment of a river suggests that a closely spaced sampling programme is essential for characterizing the sedimentary provinces within an estuary the concentrations of cs 137 metals and organic carbon in the coarse grained sediments i e 63 m are considerably lower than those in fine grained sediments thus the contribution of coarse grained sediments to the total inventory of these elements is small

role of panama uplift on oceanic freshwater balance comparison between planktic foraminiferal oxygen isotope records from the caribbean sea ocean drilling program odp site 999 and the equatorial east pacific odp site 851 suggests an increase in caribbean surface water salinity between 4 7 and 4 2 ma the modern atlantic pacific salinity contrast of about 1 became fully established at 4 2 ma as reflected by a 0 5 planktic foraminifera 18o enrichment in the caribbean sea this is interpreted as the result of restricted surface water exchange between the tropical atlantic and pacific in response to the shoaling of the central american seaway as a consequence the atlantic and pacific surface ocean circulation regime changed as did the freshwater balance between the major ocean basins simultaneous shifts in benthic carbon isotope records in the caribbean sea suggest an intensification in north atlantic thermohaline circulation these results indicate that the panamanian isthmus formation caused several new ocean atmosphere feedback mechanisms that have affected climate since the early pliocene