geochemical fingerprint of insoluble material in soil on different limestone formations abstract in the karst region near divaca slovenia soils are developed on the limestone of three geological formations se ana lipica and liburnian in each formation six soil profiles were dug limestone insoluble residua was obtained and in liburnian formation interbedded material and material filling fractures and cavities was sampled all soils have silty clay and silty clayey loam texture ph levels in the range 4 5 7 0 high organic matter content and saturation with basic cations over 50 however soils on the se ana formation are deeper and more evolved and besides as rendzic phaeozem classify also as eutric cambisol their insoluble residuum is richest in mineral part the profiles on the lipica formation are a rendzic phaeozem and the shallowest soils on the liburnian formation are either a rendzic phaeozem or a rendzic leptosol additionally the soils formed over the lipica formation are characterised by a greater portion of the small rock fragments

red mediterranean soils in jordan new insights in their origin genesis and role as environmental archives it is disputed whether terrae rossae form mainly out of the bedrock residue from allochthonous material like aerosols or by isovolumetric replacement furthermore whether they are mainly relic soils or are still forming is subject to debate these questions were addressed by comparing the geochemistry of several limestone and basalt based red mediterranean soils with lithosols on sandstone and limestone in jordan the bedrock residue was included at all test sites paleosols and initial soils on the limestone regolith of historic ruins delivered insights into the possible time frame of soil development a major reduction of elements in the soils compared to bedrock could be observed for cao in carbonaceous sio2 in arenaceous and fe2o3 and mgo in basaltic rocks all terrae rossae however are characterised by a significant increase of sio2 al2o3 tio2 fe2o3 k2o and a range of mainly metallic minor elements that cannot be derived from the bedrock a reasonable explanation could be input via aeolian transfer of minerals with clay minerals as the major carrier plus quartz this input probably originates in egypt and sudan and has remained largely unchanged over long periods growing aridity during the holocene has apparently increased the share of silt while clay deposition and soil development has been reduced at some sites metasomatic processes have contributed to soil development and might help to explain the depth of some profiles however formation of red soils during the holocene seems very limited and the red mediterranean soils may represent remains of a paleolandscape

metamorphic evolution of the attic cycladic metamorphic belt on naxos cyclades greece utilizing 40ar 39ar age spectrum measurements 40ar 39ar age spectrum analysis of phengite separates from naxos part of the attic cycladic metamorphic belt in greece indicates that cooling following high pressure low to medium temperature metamorphism m1 occurred about 50 ma ago phengite has 40ar gradients that suggest that part of the scatter observed in conventional k ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism m2 in central naxos this metamorphism m2 has overprinted the original mineral assemblages completely and is associated with development of a thermal dome excellent 40ar 39ar plateaus at 15 0 0 1 ma 11 8 0 1 ma and 11 4 0 1 ma obtained on hornblende muscovite and biotite respectively from the migmatite zone indicate that relatively rapid cooling followed the m2 event and that no significant thermal overprinting occurred subsequent to m2 toward lower m2 metamorphic grade 40ar 39ar plateau ages of hornblendes increase to 19 8 0 1 ma concomitantly the proportion of excess 40ar in the spectra increases as well we propose that the peak of m2 metamorphism occurred beween 15 0 and 19 8 ma ago k ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex and hornblende k ar ages from the same samples are in the range 12 1 13 6 ma as the latter ages are somewhat younger than most ages obtained from the metamorphic complex intrusion of the granodiorite most likely followed the peak of the m2 metamorphism the metamorphic evolution of naxos is consistent with rapid crustal thickening during the cretaceous or early tertiary causing conditions at which supracrustal rocks experienced pressures in the range 900 1500 mpa transition to normal crustal thicknesses ended the m1 metamorphism about 50 ma ago the m2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust possibly related to the migration of the hellenic volcanic ar c in a southerly direction through the area

large isotopic variability at the micron scale in shuram excursion carbonates from south australia abstract ediacaran aged 635 541 million years ago marine sediments contain a large negative carbon isotope 13 c excursion in which carbonate 13 c values reach 12 vpdb known as the shuram excursion many workers have interpreted this 13 c record as an unprecedented perturbation to the global carbon cycle leading to speculation about a causal connection to the broadly contemporaneous rise of animal life others have interpreted the 13 c signal as a product of diagenesis thereby minimizing its relevance for understanding the evolution of metazoans here we present sem imaging and in situ 13 c and 18 o values measured by secondary ion mass spectrometry sims to assess these competing hypotheses in the wonoka formation of south australia our results from the minimum of the excursion show that rounded sedimentary grains of calcite have 13 c values between 12 8 to 10 6 and 18 o values between 17 8 to 15 5 vpdb euhedral dolomite that appears to have grown unimpeded in open sedimentary pore spaces also is present these early stage dolomites are interpreted as early authigenic in origin and have 13 c values that reach 5 requiring a formation fluid with a substantially different 13 c composition from basin waters or bulk sediment together these results provide little evidence for the hypothesis that a late diagenetic overprint has generated the shuram excursion in the wonoka instead they suggest the presence of a large carbon isotopic gradient in the surface environment with shallow waters capable of precipitating carbonates with very low 13 c down to 12 and deeper shelf and or marine pore waters generating carbonates with positive carbon isotope values up to 5 because negative isotope excursions of similar magnitude are found in widely dispersed ediacaran basins it is likely that this gradient was characteristic of shelf environments of this period and that a still unknown global process led to the shuram excursion in shallow water carbonates

assessment of grain scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate bearing metamorphic rocks by ion microprobe abstract nineteen samples of metamorphosed carbonate bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a 5 15 m spot three from a regional terrain and 16 from five different contact aureoles contact metamorphic rocks further represent four groups calc silicate marble and hornfels 6 brucite marble 2 samples that contain a reaction front 4 and samples with a pervasive distribution of reactants and products of a decarbonation reaction 4 the average spot to spot reproducibility of standard calcite analyses is 0 37 2 standard deviations sd for 18 o and 0 71 for 13 c ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95 confidence interval of 0 09 0 16 for 18 o and 0 10 0 29 for 13 c using a difference of 6sd as the criterion only four of 19 analyzed samples exhibit significant intracrystalline and or intercrystalline inhomogeneity in 13 c at the 100 500 m scale with differences within individual grains up to 3 7 measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale because of relatively slow carbon isotope diffusion in calcite and dolomite differences in 13 c can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration all but 2 of 11 analyzed samples exhibit intracrystalline differences in 18 o up to 9 4 intercrystalline inhomogeneity in 18 o up to 12 5 and or disequilibrium oxygen isotope fractionations among calcite dolomite calcite quartz and calcite forsterite pairs at the 100 500 m scale inhomogeneities in 18 o and 13 c are poorly correlated with only a single mineral dolomite in a single sample exhibiting both because of relatively rapid oxygen isotope diffusion in calcite intracrystalline inhomogeneities in 18 o likely represent partial equilibration between calcite and fluid during retrograde metamorphism calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples in equilibrium with dolomite in none of six analyzed samples and in equilibrium with quartz in neither of two analyzed samples there are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other the degree of departure from equilibrium in analyzed samples is variable and is often related at least in part to alteration of 18 o of calcite during retrograde fluid rock reaction in situ sub grain scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology correlation of sub mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics reactive fluid flow and thermal histories during metamorphism

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

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

origin and metamorphism of ultrabasic rocks associated with a subducted continental margin naxos cyclades greece meta peridotites outcropping at diverent structural levels within the alpine metamorphic complex of the cycladic island of naxos were studied to re examine their metamorphic evolution and possible tectonic mechanisms for emplacement of mantle material into the continental crust the continental margin section exposed on naxos consisting of pre alpine basement and c 7 km thick mesozoic platform cover has undergone intense metamorphism of alpine age comprising an eocene m1 blueschist event strongly overprinted by a miocene barrovian type event m2 structural concordance with the country rocks and metasomatic zonation at the contact with the felsic host rocks indicate that the meta peridotites have experienced the m2 metamorphism this conclusion is supported by the similarity between metamor phic temperatures of the ultrabasic rocks and those of the host rocks maximum temperatures of 730 760 c were calculated for the upper amphibolite facies meta peridotites fo en hbl chl spl associ ated with sillimanite gneisses and migmatites relict phases in ultrabasics of diverent structural levels indicate two distinct pre m2 histories whereas the cover associated horizons have been avected by low grade serpentinization prior to metamorphism the basement associated meta peridotites show no signs of serpentinization and instead preserve some of their original mantle assemblage the geochemical aynities of the two groups are also diverent the basement associated meta peridotites retain their original composition indicating derivation by fractional partial melting of primitive lherzolite whereas serpentinization has led to almost complete ca loss in the second group the cover associated ultrabasics are interpreted as remnants of an ophiolite sequence obducted on the adjacent continental shelf early in the alpine orogenesis in contrast the basement associated meta peridotites were tectonically interleaved with the naxos section at great depth during the alpine collision and high p t metamorphism their emplacement at the base of the orogenic wedge is inferred to have involved isobaric cooling from tempera tures of c 1050 c within the spinel lherzolite field to eclogite facies temperatures of c 600 c

using sims to decode noisy stratigraphic δ13c variations in ediacaran carbonates abstract carbonate carbon isotope 13ccarb chemostratigraphy is a valuable tool in precambrian stratigraphic correlation the effectiveness of this tool rests on the assumption that 13ccarb data record global seawater signals however in some cases 13ccarb data exhibit rapid and noisy stratigraphic variations that may have been influenced by authigenic or diagenetic carbonate minerals to assess the contribution of non primary minerals towards bulk carbonate carbon isotope values we acquired sims secondary ion mass spectrometry 13ccarb data electron microscopic data and cl cathodoluminescence microscopic data from two ediacaran successions the lower member ii of the doushantuo formation in south china and the mooifontein member of the zaris formation in southern namibia the doushantuo samples came from a stratigraphic interval with noisy meter scale 13ccarb variations of up to 10 whereas the mooifontein member is characterized by consistent 13ccarb values with limited meter scale variations of less than 4 our data show that the meter scale stratigraphic variations in 13ccarb are also mirrored in the sims data at m mm scales in both doushantuo and mooifontein samples in the doushantuo samples sims 13ccarb values of authigenic calcite vary by up to 10 over m mm scales and can be either higher or lower than those of the co existing dolomite matrix which also appears to be affected by authigenic carbonate on the basis of petrographic observation bulk sample 13ccarb values measured on powders microdrilled from the same sims specimens are within the range of sims 13ccarb values thus we infer that bulk sample 13ccarb values of doushantuo samples represent mixtures of different carbonate components the doushantuo and mooifontein sims 13ccarb data validate the traditional method of using chemostratigraphic consistency to evaluate authigenic diagenetic alteration but given that secondary phases may be 13c enriched relative to matrix carbonate caution is warranted when taking maximum values to approximate primary chemostratigraphic trends

paleopedology of terrae rossae rodoxeralfs from quaternary calcarenites in nw morocco abstract selected terrace rossae or rhodoxeralfs from calcarenites in all probability of mid pleistocene age in the vicinity of rabut show a strong mineral weathering and a considerable to extensive formation of clay minerals especially of kaolinites main sources of pedogenic kaolinites mostly of a disordered structure and poor cristallinity are primary feldpars 2 m and smectites 2 0 2 and

mineral magnetic properties of an alluvial paleosol sequence in the maya lowlands late pleistocene holocene paleoclimatic implications abstract in the maya lowlands region along the usumacinta river late pleistocene holocene profiles exhibit sedimentary characteristics and soil formation processes as a result of environmental conditions and human environmental interactions here we report a comprehensive environmental magnetic investigation on paleosols and sediments at the tierra blanca archaeological site which shows clear evidences of human occupation the pedogenetical magnetic properties were characterized by rock magnetism studies to determine the composition concentration and domain size distribution of magnetic minerals the late pleistocene paleosols were formed under the influence of a humid climate as shown by the presence of recent fine hematite formation directly related to reduction oxidation processes during gleysol development the transition from early to middle holocene was obtained from a paleovertisol dated as 2 34 2 3 ka which showed a marked heterogeneity in its magnetic parameters due to continuous argilloturbation processes the environmental conditions retrieved indicate the presence of a drought period around 5 5 ka the upper two paleosols were less developed and seems to be strongly affected by human activities during the maya classic period dated between 1 14 and 0 97 ka these soils were formed under more humid conditions and yielded a magnetic mineralogy hematite magnetite maghemite due to incipient weathering and anthropic disturbance

oxygen isotope thermometry of quartz al 2 sio 5 veins in high grade metamorphic rocks on naxos island greece diffusion models predict that peak metamorphic temperatures are best recorded by the oxygen isotope fractionation between minerals in a bi mineralic rock in which a refractory accessory mineral with slow oxygen diffusion rate is modally minor to a mineral with a faster diffusion rate this premise is demonstrated for high grade metamorphism on the island of naxos greece where quartz kyanite oxygen isotope thermometry from veins in high grade metamorphic pelites gives temperatures of 635 690 c these temperatures are in excellent agreement with independent thermometry for the regional m2 peak metamorphic conditions and show that the vein minerals isotopically equilibrated at the peak of metamorphism quartz sillimanite fractionations in the same veins give similar temperatures 680 35 c and suggest that the veins grew near to the kyanite sillimanite boundary corresponding to pressures of 6 5 to 7 5 kbar for temperatures of 635 685 c by contrast quartz kyanite and quartz biotite pairs in the host rocks yield lower temperature estimates than the veins 590 600 and 350 550 c respectively these lower apparent temperatures are also predicted from calculations of diffusional resetting in the polyphase host rock system the data demonstrate that bimineralic vein assemblages can be used as accurate thermometers in high temperature rocks whereas retrograde exchange remains a major problem in many polymineralic rocks

evidence for volcanic ash fall in the maya lowlands from a reservoir at tikal guatemala powder x ray diffraction and petrographic analyses of reservoir sediments from tikal guatemala have identified significant quantities of decomposed volcanic ash in the form of smectite and euhedral bipyramidal quartz crystals x ray fluorescence trace element content analysis was used to eliminate distant sahara sahel and antilles sources the zr y and ni cr ratios of reservoir sediment from tikal are consistent with a source from central american volcanism e g guatemalan and salvadoran ams radiocarbon dating of the smectite and crystalline quartz rich reservoir sediments show that volcanic ash fell during the preclassic classic and postclassic maya cultural periods it may now be possible to develop an effective chronology of ash fall at tikal and the greater peten published by elsevier ltd

zircon in amphibolites from naxos aegean sea greece origin significance and tectonic setting we report u pb zircon ages of c 700 550 ma 262 220 ma 47 38 ma and 15 14 ma from amphibolites on naxos island in the aegean extensional province of greece the zircon has complex internal structures based on cathodoluminescence response zoning and crosscutting relationships a minimum of four zircon growth stages are identified inherited core magmatic core inner metamorphic rim and an outer metamorphic rim trace element compositions of the amphibolites suggest igneous differentiation and crustal assimilation zircon solubility as a function of saturation temperatures zr content and melt composition indicates that the zircon did not originally crystallize in the mafic bodies but was inherited from felsic precursor rocks and subsequently assimilated into the mafic intrusives during emplacement zircon inheritance is corroborated by the complex xenocrystic nature of the zircon in one sample ages of c 700 550 ma and 262 220 ma are assigned to inherited zircon available geochemical data suggest that the 15 14 ma metamorphic rims grew in situ in the amphibolites corresponding to a high grade metamorphic event at this time however the geochemical data cannot conclusively establish if the c 40 ma zircon rims also grew in situ or whether they were inherited along with the xenocrystic cores two scenarios for emplacement of the mafic intrusives are discussed i intrusion during late triassic to jurassic ocean basin development of the aegean realm in which case the 40 ma zircon rims would have grown in situ and ii emplacement in the miocene as a result mafic underplating during large scale extension in this case only the 15 14 ma metamorphic outer rims would have formed in situ in the amphibolitic host rocks

quantification of soil erosion rates related to ancient maya deforestation we used seismic and sediment core data to quantify soil erosion rates for the past 6000 yr in the closed catchment of lake salpeten in the tropical lowlands of northern guatemala the region was affected by ancient maya land use from before ca 1000 b c to a d 900 this period of human impact coincided with deposition in the lake of a detrital unit maya clay as much as 7 m thick that contrasts sharply with the relatively organic rich gyttja deposited both before and after maya occupation of the watershed the greatest soil loss with mean sustained values of 1000 t km2yr 1 occurred in the middle and late preclassic periods 700 b c to a d 250 associated with relatively low maya population densities soil erosion slowed during the period of maximum population density in the late classic period a d 550 830 indicating a decoupling between human population density and soil erosion rate the most rapid soil loss occurred early during initial land clearance suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes

stability and instability on maya lowlands tropical hillslope soils abstract substantial lake core and other evidence shows accelerated soil erosion occurred in the maya lowlands of central america over ancient maya history from 3000 to 1000 years ago but we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade this study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in nw belize the research aim is to understand soil formation long term human impacts on slopes and slope stability over time and explore ecological implications we studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts all of our soil catenas except for one deforested from old growth two years before contain evidence for about 1000 years of stable tropical forest cover since maya abandonment we characterized the physical chemical and taxonomic characteristics of soils at crest shoulder backslopes footslopes and depression locations analyzing typical soil parameters chemical elements and carbon isotopes 13 c in dated and undated sequences four footslopes or depressions in areas of high ancient occupation preserved evidence of buried clay textured soils covered by coarser sediment dating from the maya classic period three footslopes from areas with scant evidence of ancient occupation had little discernable deposition these findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the maya period using major elemental concentrations across a range of catenas we derived a measure ca mg al fe mn of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas we found very low ratios in clearly older buried soils in footslopes and depressions and on slopes that had not undergone ancient maya erosion we found high ca mg al fe mn values on slopes with several lines of evidence that suggest relative youth soils possibly formed since maya abandonment carbon isotopes 13 c also provide some evidence of past vegetation change on slopes we found strong evidence for maize or other alien c 4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for c 3 species like tropical trees on the backslopes and other crest shoulders the fact that steep slopes preserved no evidence of c 4 species inputs may mean that the ancient maya maintained forests here alternatively ancient maya land uses eroded slopes with the 13 c signatures detected today being the result of more recent soil development under forest over the last millennium additional evidence that these soils are recent in age includes elevated ca mg al fe mn values skeletal soil profiles and low soil magnetic susceptibility besides the evidence for truncating backslopes and aggrading footslopes the ancient maya built agricultural terraces that accumulated soils and altered drainage all these ancient maya slope alterations would have influenced modern tree distributions because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient maya changed

laminated soil carbonate rinds as a paleoclimate archive of the colorado plateau abstract recent work suggests that the c and o isotope composition of laminated soil carbonate rinds can provide high resolution 100 s yr sample information about hydrologic processes and vegetation over tens of thousands of years however while this archive can potentially provide quantitative reconstructions most interpretations have thus far been qualitative in this study we show how modern soil data and clumped isotope paleothermometry can be leveraged to constrain the conditions of rind formation for a sample from the western colorado plateau utah usa we can thus quantitatively interpret rind isotope values as vegetation composition c3 plants and soil water oxygen isotope composition 18osoil water over 35 5 ka we validate the approach by demonstrating consistency between our record and other paleoarchives from the western usa laminated soil carbonate rinds therefore represent a new avenue for sub millennial scale quantitative investigations of paleoclimatology paleoecology archeology and modeling questions down to the level of individual soils

soils in the mediterranean region what makes them different mediterranean climates are characterized by winter rains with some months of excess rainfall over evatranspiration warm and dry summer months with moisutre deficits drying out soils and their annual vegetation xeric moisture regime they are found on western parts of all continents between the cooler temperature zone and the hot dry desert zone the largest mediterranean region surrounding the mediterranean sea extends over 4 300 000 km2 and exhibits a wide variety of soils and geo ecosystems characteristics landscape attributes are the high proportion of mountains with sleep slopes significant additions of saharan desert dust to practically all soils of the region and a large proportion of limestone and other calcareous rocks as soil parent materials characteristics soil behavior features are moderate weathering with pervection leaching lessivage of mostly 2 1 clays into b horizons xeralfs luvisols hematite induced reddening of the clays due to summer dehydration of free iron oxyhydroxides carbonate dissolution and reprecipitation with prevalence of calcic horizons xerolls calcisols in semiarid regions and development of vertisols mostly in lowlands where deep layers of swelling cracking clays have sedimented shallows soils on nearly bare slopes mostly a result of erosion subsequent to deforestation are frequent leptosols cambiosols inceptisols entisols red or brown mediterranean soils are no longer used as a separate classification group in modern well defined soil property controlled taxonomies soil taxonomy fao system but were partially replaced by duchaufour s term fersiallitic soils in some classification systems terra rossa continues to be used in some classification for hard limestone derived red soils mostly shallow the effects of man s past and current interference with the lanscape are pervasive in most regions and predictions for possible future effects on the soils and ecosystems due to greenhouse gas induced warming and rainfall change are partly negative partly still too uncertain

mechanisms of oxygen isotopic exchange and isotopic evolution of 18 o 16 o depleted periclase zone marbles in the alta aureole utah insights from ion microprobe analysis of calcite oxygen isotope ratios have been measured by ion microprobe and millimeter scale dental drill along detailed sampling traverses across the boundary between periclase bearing 18o 11 8 and periclase free 18o 17 2 marble layers in the periclase per zone of the alta stock aureole utah these data define a steep coherent gradient in 18o that is displaced a short distance 4 cm into the periclase free cal fo layer sem and ion microprobe analyses show two isotopically and texturally distinct types of calcite at the grain scale clear well polished calcite grains are isotopically homogeneous within analytical uncertainty 0 27 2sd more poorly polished pitted texturally retrograde turbid looking calcite has lower and more variable 18o values and replaces clear calcite along fractures cleavage traces or grain boundaries despite significant lowering of the 18o values in calcite throughout both layers during prograde metamorphism ion microprobe analyses indicate that individual clear calcite grains are now isotopically homogeneous across the entire gradient in 18o diffusion calculations indicate that conservative time scales required for isotopic homogenization of calcite grains by volume diffusion 30 000 62 000 years at 575 600 c exceed significantly the timescale 1 250 years estimated for the prograde development of the 18o gradient at the boundary between these two marble layers the ion microprobe data and these diffusion calculations suggest instead that surface reaction mechanisms accompanying recrystallization are responsible for the observed oxygen isotope homogeneity of these calcite grains thus the ion microprobe data are consistent with the formation of calcite in oxygen isotope exchange equilibrium with infiltrating fluid during prograde reaction and recrystallization

a 550 year old plinian eruption at el chichon volcano chiapas mexico explosive volcanism linked to reheating of the magma reservoir 1 some 550 years ago 1320 1433 a d a powerful plinian eruption at el chichon volcano in southern mexico produced a widespread pumice fall deposit we subdivided the deposit into three parts on the basis of structural and textural characteristics pumice lithology and density granulometry and petrologic geochemical attributes the deposit covers an area of 1500 km2 within the 1 cm isopach and has a minimum estimated bulk volume of 2 8 km3 1 1 km3 dense rock equivalent dre its eruptive column reached an altitude of 31 km consideration of field evidence the presence and nature of mafic enclaves and chemical data strongly suggest that the 550 year b p eruption is linked with the intrusion of a high temperature basaltic magma into preexisting but stagnated trachyandesitic magma beneath el chichon thorough mixing of the two magmas produced a compositionally uniform hybrid trachyandesite magma average sio2 55 3 wt which subsequently underwent crystal growth and gas exsolution ultimately overpressurizing the zoned magmatic system to erupt explosively on the basis of el chichon s known eruptive history the intrusion mixing event occurred sometime after the 900 year b p eruption the hybrid magma had a preeruption temperature of 820 830 c and was water undersaturated 5 6 wt h2o at pressures of 2 2 5 kbar

repeated recharge assimilation and hybridization in magmas erupted from el chichon as recorded by plagioclase and amphibole phenocrysts abstract compositional and isotopic zoning patterns in plagioclase and amphibole phenocrysts from el chichon record multiple cycles of country rock assimilation magma injection hybridization and mixing laser ablation icp ms and electron microprobe analyses of plagioclase crystals from 7 eruptions spanning 3100 years reveal four types of zoning these compositional and isotopic zones are often associated with textural changes observed in the crystals in thin section e g sieved or patchy regions amphiboles are frequently zoned in al and si and in two magmas may have clinopyroxene rims interestingly most plagioclase show multiple and repeated zoning patterns moreover all magmas contain all zoning patterns and textures and crystals with substantially different sequences of zones occur within mm of one another the most reasonable explanation for the origin of these textures is a frequently recharged chamber plagioclase zones with increasing anorthite contents an and decreasing 87sr 86sr ratios record injection by a hotter possibly wetter and more primitive magma lower 87sr 86sr ratio zones with decreasing an and increasing 87sr 86sr ratios record assimilation of country rock and or hybridization of the host and injected magmas injection of hot magma may provide the heat for country rock assimilation changes in an without corresponding changes in 87sr 86sr ratio likely record slight variations in pressure or temperature during crystallization or the far field thermal effects of magma injection variations in 87sr 86sr ratio unaccompanied by anzoning record assimilation of country rock amphibole zoning patterns also record periodic heating events amphibole with clinopyroxene rims record episodes where the magma was heated beyond the amphibole stability field bulk compositional homogeneity and the juxtaposition of many crystals with disparate zoning patterns in single pumice require the magmatic system to be well mixed strontium diffusion rates indicate that the plagioclase zoning patterns cannot have persisted at magmatic pressures and temperatures for more than 500 years thus cycles of injection and assimilation occur on timescales equal to or shorter than the eruption recurrence interval long term compositional and isotopic homogeneity indicate that there is a balance between recharge assimilation and crystallization

dynamic evolution of the ediacaran ocean across the doushantuo formation south china abstract oceanic redox conditions and atmospheric oxygenation likely played a crucial role in the evolution of macroscopic multicellular eukaryotes during the early ediacaran period however the oxidation mechanism and magnitude of the ediacaran ocean atmosphere system remain controversial to constrain the oceanic redox conditions and the contemporaneous oxygenation of the atmosphere we present a comprehensive investigation of redox sensitive elements e g mo and u fe speciation and s isotopes of pyrite from the platform slope and basin sections across the doushantuo formation in south china our results suggest a redox stratified ediacaran ocean with a fluctuating chemocline from the slope to platform location across the doushantuo formation in particular euxinic intermittently euxinic conditions developed not only at the platform and slope but also in the deep basin furthermore these euxinic conditions indicate that high sulfate concentrations may have accumulated not only at the ending of the ediacaran doushantuo formation but also at the middle and beginning thus these results suggest that the extensive euxinic conditions associated with the continuous oceanic sulfate input were in response to progressive oxygenation of the atmosphere during the early ediacaran period integrated with previously published results if the dissolved organic carbon doc reservoir existed different mechanisms may be responsible for the oxidation of deep ocean in each part of the studied sections across the doushantuo formation one mechanism is oxidation by sulfate through a bacterial sulfate reduction bsr process under anoxic conditions another mechanism is oxidation by dissolved free oxygen under oxic suboxic conditions finally a dynamic evolution model of the ediacaran ocean atmosphere system across the doushantuo formation south china was suggested

pedosediments of karstic sinkholes in the eolianites of ne yucatan a record of late quaternary soil development geomorphic processes and landscape stability abstract the pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes are still poorly understood we have discovered and studied thick pedosediments in karst pockets developed in late pleistocene lithified calcareous dunes eolianites in the ne coast of the yucatan peninsula the morphological geochemical and mineralogical characteristics of the pocket fills were interpreted as a record of pedogenesis and geomorphic dynamics that shaped the soil mantle during the holocene sand fraction mineralogy and the zr ti ratio indicated a mixed origin of the soil parent material volcanic and granitic metamorphic components redeposited in the lithoral and coastal environments were identified within the soil matrix primary minerals were transformed by weathering and caused desilicification accumulation of clay hydroxy interlayered vermiculite and kaolinite and dithionite citrate bicarbonate extractable iron oxides fed reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed this set of processes points to a continuous phase of humid pedogenesis several thousand years long in the early middle holocene however the development of thick recalcified pedosediments in the pockets contrasting with the thin background rendzinas requires active soil redeposition during a late phase of geomorphic activity the available accelerator mass spectrometry ams radiocarbon date indicates that the switch of the erosion sedimentation processes could be related to ancient maya land use impact

a garnet zircon oxygen isotope record of subduction and exhumation fluids from the franciscan complex california tectonic blocks of high grade metamorphic rock hosted by the franciscan me lange commonly preserve textural and geochemical evidence for metasomatism and blueschist facies overprinting within a subduction zone these exhumation events can obscure information on the nature of subduction fluids at depth that might otherwise be preserved by these rocks in this tectonic setting cation and oxygen isotope zoning in garnets from eclogite and garnet hornblende rocks with minimal textural evidence of retrogression reveals separate prograde and retrograde fluid histories garnet cores preserve a homogeneous prograde oxygen isotope history with both high do 11o and low 4o values in different samples probably recording altered ocean crust protolith compositions multiple episodes of garnet resorption and regrowth record a dramatically changing bulk oxygen isotope ratio resulting in 6 7o neoformed garnet rims with sharp core rim boundaries in both samples matrix omphacite and hornblende are in profound oxygen isotope disequilibrium with garnet cores but are in equilibrium with garnet rims despite the appearance of overall textural equilibrium in thin section this cryptic metasomatism found in samples from different locations within the franciscan complex brings into question existing thermobarometry on non inclusion phases for this complex as well as interpretations based on whole rock geochemical data zircon ages and oxygen isotope equilibrium with late forming garnet are consistent with postmetasomatic formation of zircon the ability of garnet and zircon to record multiple fluid events and tie them to p t t fluid history is a powerful tool in gaining an improved understanding of the complex fluid environments within subduction zones

red mediterranean soils in some karstic regions of taurus mountains turkey abstract red soils are found along fractures and between bedding surfaces in karstic regions of both mediterranean and aegean regions of turkey these soils are very unique and information on pedogenesis in karstic regions are rather limited detailed field works were carried out at 17 locations soil profiles were examined at 14 sites and 7 of these were reported here soil samples from thea and b horizons of these soils are used to detailed characterization analyses in the laboratory occurrence of normal soil profiles were unusual in the study regions the fractured structure of limestone leads to unusual water and air circulation when water penetrates into rock fissures and holes and diffuses into sedimentary layers in situ weathering processes take place rock fissures and holes may also be filled in by the transport of soil materials from higher elevations sedimentary petrology and mineralogy of limestones are the factors that control the course of the pedogenesis oxidation of fe especially sulfides pyrite accelerates the soil formation in limestones soils are not present on massive an fractured or fissured limestones and thin and stony red soils are common only at the bottom parts of v shaped dolines however soils are thick and common within the materials that have alternating marl and sandy silty layers vertical movement of soil particles towards the deeper parts of te limestone tkes place as a result of the widening of the lapies which are mostly formed along the fractures most of the red soils in the studied karstic regions were likely developed during the tertiary and ot and humid periods of the quaternary epochs large body of soils which are found in deep limestones suggest their formation under paleochimatic environments

textural and isotopic development of marble assemblages during the barrovian style m2 metamorphic event naxos greece a detailed petrological analysis of the marble assemblages observed within the m2 metamorphic complex on naxos is presented two distinct periods of mineral growth are documented the first is associated with prograde m2 metamorphism and the second with retrograde m2 metamorphism occurring during ductile extensional thinning of the complex the textural and miner alogical characteristics and the carbon and oxygen isotope compositions of each generation are described and the p t xco2 conditions at which these two mineral generations were stable and the compositions of the fluids present during metamorphism are characterised whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution the retrograde mineral generation is shown to have grown as a result of the infiltration of a water rich fluid phase that transported silica al2o3 na2o and feo into the host rocks this observation together with the stable isotope compositions of the retrograde calcite and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas t 600 c of the metamorphic complex suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures the existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on naxos because many of the unusually low 18o compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde m2 fluids rather than with prograde fluids

phytoliths stable carbon isotopes and micromorphology of a buried alluvial soil in southern mexico a polychronous record of environmental change during middle holocene abstract the reconstruction of the maya lowlands vegetational history and its paleoecological implications during the middle late holocene was carried out using phytolith analysis and organic matter stable isotopic ratios three sections located in a terrace of the usumacinta river were studied tierra blanca i tierra blanca ii and el pochote they consisted of a series of alluvial sediments alternating with paleosols that contained artifacts belonging to the formative classic and postclassic periods according to the mesoamerican chronology our results showed that the middle holocene paleosols had well developed vertic features with 16 13c values which evidence seasonal semiarid conditions however phytolith content recorded a predominance of c3 plants and paleosol micromorphology showed a set of features related to an alternation of humid and drier conditions therefore stable isotope composition reflects the integral signal of the last period of soil formation phytoliths and soil micromorphology correspond to a more extensive record that represents the successive stages of pedogenetic and environmental changes

calculation of oxygen isotope fractionation in metal oxides abstract a theoretical model calculating the thermodynamic isotope factors of oxygen in metal oxides of geochemical interest is presented for temperatures between 0 and 1200 c on the basis of the modified increment method the following order of 18o enrichment is obtained cassiterite rutile magnetite ilmenite ulvospinel hematite uraninite chromite corundum spinel the results are expressed as 103 in a 106 t2 b 103 t c which compare well with existing theoretical experimental and empirical calibrations on quartz oxides and oxides water systems the present calculations enable not only estimation of the oxygen isotope composition of fluids from which the metal oxides were precipitated when independent temperature information is available but can also be applied as oxygen isotope geothermometers to igneous and metamorphic rocks

cultural and climatic history of coba a lowland maya city in quintana roo mexico abstract lake coba within the archaeological site of coba provides evidence bearing on lowland maya development palynological and geochemical data record multidecadal precipitation cycles from a 8 80 m 8370 yr lake sediment sequence terminating on bedrock late classic sedimentation rates are rapid but an anthropogenically derived colluvium layer is lacking initial vegetation was medium semi deciduous and swamp forest forest clearance began 1650 b c early preclassic and maize first occurred at 850 b c middle preclassic lakeside milpas existed until a d 720 late classic and then were moved from the city center as urbanization intensified and lake coba was diked as a reservoir coba was at most briefly vacated during the classic collapse and was abandoned after a d 1240 although some habitation persisted the paleoecological record matches the archaeological history for coba but pervasive disturbance muted the climatic signal as the late classic drought is barely evident the question whether economic trees were maintained within the city is unresolved maize cultivation allowed the maya to develop a complex society and support a large population but dependence on maize was ultimately doomed by variable rainfall precipitation in extreme years was insufficient to support crops while native vegetation was not directly affected by drought that devastated maya agriculture

dwindling vanadium in seawater during the early cambrian south china abstract elemental vanadium v an essentially redox sensitive metal in seawater has had a significant impact on the understanding of the evolution of the atmosphere ocean system throughout the history of the earth in fact the geochemical cycle of v in early cambrian seawater may have had an influence on the chengjiang biota in south china however it has not yet been well established given the authigenic vanadium accumulation is sensitive to the redox conditions of seawater here to constrain the geochemical cycle of v in seawater during the early cambrian the mo u and total organic carbon toc distributions with high resolution samples from both the outer shelf and slope facies e g the duoding and longbizui sections are applied to evaluate the redox conditions of ambient seawater the mo u relationships indicate that the redox conditions of the mid depth seawater evolved in a systematic way in south china transitioning from an fe mn reduction zone to anoxic intermittently euxinic states and then to oxic conditions during the early cambrian as a consequence the authigenic v enrichment constrained by the marine redox conditions was mainly controlled by the fe mn particulate shuttle and the reduction and adsorption of organic matter in anoxic euxinic conditions however the decoupling among v mo u and toc under anoxic euxinic conditions suggests a dwindling vanadium concentration in the early cambrian seawater of south china the scavenging efficiency of v from seawater is much higher than those of mo and u under anoxic euxinic conditions ultimately these trace elements e g mo u and especially v in seawater could effectively be regulated and adjusted to a reasonable level under the widespread anoxic euxinic conditions the drawdown of trace elements in seawater might provide an early stage preparation of the marine environment for the subsequent chengjiang biota

a preliminary stable isotope study on mogok ruby myanmar the primary occurrence of ruby in the mogok area northern myanmar is exclusively found in marble along with spinel forsterite bearing marble and phlogopite graphite marble these marble units are enclosed within banded biotite garnet sillimanite oligoclase gneisses samples of these marbles collected for c o stable isotope analysis show two trends of 13c 18o variation resulting most likely from fluid rock interactions ruby bearing marble and phlogopite graphite marble followa trend with coupled c o depletion whereas spinel forsterite bearing marble follows a 18o depletion trend with relatively constant 13c values ruby formation might have resulted from co2 rich fluid rock interaction while spinel forsterite bearing marble was genetically related to co2 poor fluid rock interaction both fluids may have arisen from external sources based on graphite raman spectral thermometry the estimated temperature for phlogopite graphite marble and probably ruby bearing marble was lower than 607 c and for spinel forsterite bearing marble lower than 710 c contrasting c o diffusion between graphite ruby spinel forsterite and calcite local variations of isotopic compositions of newly formed minerals as a result of non pervasive fluid infiltration and open system isotopic disturbance during cooling may have affected c o isotopic fractionations between minerals the estimated high formation temperatures for ruby and spinel forsterite imply that the parental fluidsmay have been related to nearby igneous intrusions and or metamorphic processes whether these two types of fluid were genetically related is unclear based on the present data

the use of pozzolanic materials in maya mortars new evidence from rio bec campeche mexico the use of pozzolanas to improve the performance of lime mortar is usually regarded as a major contribution of the greco roman civilizations to mortar technology while this remains unquestioned recent investigations have shown that this practice was also known in mesoamerica before the spanish conquest the mortars produced in the maya lowlands in particular have been shown to contain various compounds similar to those formed as a result of the reaction between lime and pozzolanas such as volcanic ash or other siliceous and or aluminous materials however until recently petrographic studies had failed to present direct evidence that the formation of these compounds was due to the addition of pozzolanas rather than to the use of a natural hydraulic lime the microscopic analysis of mortar samples from the archaeological site of rio bec in southeastern campeche provides this evidence the identification of pyroclastic material in the form of unaltered glass shards confirms for the first time the use of pozzolanic materials in ancient maya mortars furthermore the analysis suggests the use of other materials that potentially acted as pozzolanas such as phytoliths and argillaceous inclusions the purpose of this paper is to present these new data and to discuss their significance for the understanding of maya mortar technology

ion microprobe survey of the grain scale oxygen isotope geochemistry of minerals in metamorphic rocks abstract the oxygen isotope compositions of calcite diopside dolomite forsterite garnet k feldspar kyanite plagioclase quartz and wollastonite were analyzed in suites of contact and regional metamorphic rocks using an ion microprobe spatial resolution was 10 m precision measured as the standard deviation of working standards averaged over the entire project was 0 13 0 18 for three carbonate standards and 0 11 0 12 for two silicate standards a total of 1176 analyses excluding standards were made of 73 minerals in 23 samples both intercrystalline and intracrystalline variability in 18 o is greater in contact than in regional metamorphic rocks of 27 minerals analyzed in contact metamorphosed rocks 70 exhibit statistically significant grain to grain variability in 18 o over areas 1 41 cm 2 with the largest range in silicates and carbonates in a single sample of 7 4 forsterite and 10 6 dolomite of 88 grains analyzed in two or more places in contact metamorphosed rocks 32 exhibit statistically significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of 3 1 forsterite and 10 1 dolomite in contrast 44 of 45 minerals in regional metamorphic rocks exhibit significant grain to grain variability in 18 o over areas 1 17 cm 2 with the largest range in silicates and carbonates in a single sample of only 1 1 plagioclase and 0 9 calcite only 6 of 144 grains analyzed in two or more places in regional metamorphic rocks exhibit significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of only 1 5 diopside and 0 7 calcite the difference in intercrystalline and intracrystalline variability in 18 o between contact and region metamorphic rocks is explained by the longer duration and slower reaction rates of regional metamorphism rather than to differences in temperature there is no significant difference in intercrystalline and intracrystalline variability in 18 o in regional metamorphic rocks among samples from the biotite garnet and kyanite zones calcite inclusions in forsterite and calcite and quartz inclusions in garnet either have 18 o that is statistically indistinguishable from 18 o of the same mineral occurring as nearby matrix grains or have statistically significant lower 18 o no reversed isotope fractionations were measured between coexisting mineral pairs minerals in individual samples however exhibit a wide range in the degree to which they attained and preserve oxygen isotope fractionations consistent with metamorphic temperatures recorded by mineral equilibria processes that account for grain scale departures from isotope exchange equilibrium include a overstepping of prograde mineral reactions b growth zoning in low diffusivity minerals c interaction of rocks with fluids at the peak of metamorphism and or during cooling d retrograde mineral reactions and e closed system isotope exchange between coexisting minerals during cooling this study provides new information about 1 the degree to which a variety of textural changes experienced by rocks during metamorphism are associated with changes in 18 o 2 oxygen isotope homogenization at the outcrop scale among contrasting lithologies 3 changes in 18 o with increasing grade of regional metamorphism and 4 time scales of metamorphic process

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

iron oxide mineralogy of terra rossa and its genetic implications abstract fe d fe d fe t hematite geothite ratios and al substitution in hematite and goethite were found to vary to a rather limited extent in 48 terra rossa samples from various locations around the world this seems to indicate a rather specific pedoenvironment in which terra rossa is formed it is suggested that this pedoenvironment is characterized by an association of mediterranean climate high internal drainage due to the karstic nature of a hard limestone and neutral ph conditions under those conditions relatively high amounts of fe are released fe d fe t ca 0 7 from autochthonous and or allochthonous primary fe sources followed by preferential formation of hematite over goethite both having a medium level of al substitution the close association between terra rossa and the underlying limestone must therefore be seen in the role the rock plays for the water and air regimes of the soil rather than in its material characteristics except for soil ph neither an fe content in the limestone insufficient to explain the fe content of the solum nor the addition of eolian or alluvial material can therefore be used as an argument against a genetic relationship between terra rossa and its underlying limestone

reconstruction of early cambrian ocean chemistry from mo isotopes the neoproterozoic cambrian transition was a key time interval in the history of the earth especially for variations in oceanic and atmospheric chemical composition however two conflicting views exist concerning the nature of ocean chemistry across the precambrian cambrian boundary abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late ediacaran while other studies provide seemingly conflicting evidence for anoxic deep waters with ferruginous conditions fe ii enriched persisting into the cambrian here two early cambrian sedimentary platform and shelf slope sections in south china were investigated to trace early cambrian ocean chemistry from mo isotopes the results reveal that early cambrian sediments deposited under oxic to anoxic euxinic conditions have 98 95mo values ranging from 0 28 to 2 29 which suggests that early cambrian seawater may have had 98 95mo values of at least 2 29 similar to modern oceans the heaviest and relatively homogeneous 98 95mo values were recorded in siltstone samples formed under completely oxic conditions which is considered that mn oxide free shuttling was responsible for such heavy 98 95mo value further combined with fe species data and the accumulation extent of mo and u the variation of 98 95mo values in the two studied sections demonstrate a redox stratified ocean with completely oxic shallow water and predominantly anoxic even euxinic deeper water having developed early on which eventually became completely oxygenated this suggests that oceanic circulation at the time became reorganized and such changes in oceanic chemistry may have been responsible for triggering the cambrian explosion of biological diversity

progressive oxidation of anoxic and ferruginous deep water during deposition of the terminal ediacaran laobao formation in south china abstract the laobao formation a black chert sequence was deposited in deep water in the terminal ediacaran nanhua basin the chert samples have finely laminated fabric and have no distinct recrystallization or metasomatic relict texture there is an extremely limited detrital component and no obvious hydrothermal influence therefore the chert appears to be an authigenic deep water precipitate the trace elements in the chert were mainly derived from seawater and thus could be a relatively unique proxy for late precambrian seawater conditions redox sensitive trace elements and relevant ratios were used to reconstruct the depositional environment of the chert sequence combined with iron species results of the laobao formation enrichments in redox sensitive trace elements u v mo depleted mn very low th u ratios 7 9 and v v ni 0 6 ratios suggest an overall anoxic and ferruginous conditions over the deposition of the chert the pyrite sulfur isotope compositions are between 15 4 and 11 0 and show a decreasing trend toward the top of the section possibly implying sulfate concentration gradually increased in the terminal ediacaran nanhua basin which is consistent with implication of their pyrite framboid diameter characteristics our data confirm that deep water in the nanhua basin was still anoxic and ferruginous and it was progressively oxidized during the terminal ediacaran period which could create necessary conditions for the emergence and rapid evolution of multicellular metazoans

reprint of impacts of mayan land use on laguna tuspan watershed peten guatemala as seen through clay and ostracode analysis abstract most of the cities built by the mayas in the peten area in the central yucatan peninsula were abandoned 1200 to 1000 years ago the phenomenon is sometimes un appropriately called the collapse of the maya civilization its main causes are still debated ranging from climatic according to the occurrence of severe or modest droughts to societal in the form of environmental mismanagement of the environment in both processes it is inferred that stress triggered the formation in many peten lake sediments of erosional clay deposits known as maya clays this work presents a high resolution multi proxy study of maya clays in lacustrine sediments from laguna tuspan near the archaeological site of la joyanca micropaleontological ostracodes mineralogical clay minerals and geochemical bulk elemental composition and stable isotopes in organic carbon records reveal three different phases of soil erosion throughout the last 5300 years the oldest phase from 5281 to 2998 cal yr bp i e 3331 1048 bc is characterized by successive natural and moderate soil erosion deposits which follow climatic variations recorded in the american tropical belt the time interval between 2998 and 1281 cal yr bp i e 1048 bc and ad 661 contains four distinct erosional layers which according to clay mineralogy are indicative of both increased erosion of the regolith and strong soil loss the most recent also the most massive deposit of maya clay ends around 1281 cal yr bp ad 661 that is some 200 years before the so called maya collapse in the peten area recent archeological fieldwork studies indicate that a population mobility took place into the city of la joyanca from its hinterland by the early late classic period ca ad 600 that is at the end or just after this erosion episode and well before the occurrence of the terminal classic postclassic ad 800 1250 drastic climatic changes shifts in environmental management by the local society and timing of urbanization may explain environmental changes better than droughts per se

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

oxygen isotope thermometry based on a refined increment method and its application to granulite grade rocks from sri lanka abstract in this paper we first present a revision of the increment method a semi empirical technique which allows the calculation of o isotope fractionation factors between all silicates provided their structure and chemical composition is known for the temperature dependency the experimentally calibrated high pressure mineral calcite fractionation factors of chiba et al 1989 are taken as a basis then this method is applied to granulite facies parageneses from sri lanka including quartz k feldspar sillimanite garnet pyroxenes amphiboles cordierite magnetite and ilmenite it can be shown that o isotope equilibration occurred at granulite facies conditions at about 830 c due to static recrystallization locally retrograde re equilibration occurred also at much lower temperatures due to late d4 in most cases however o isotope disequilibria resulted from retrograde oxygen intracrystalline diffusion it can be proved by model calculations that the o diffusion data for water saturated systems reported in the literature are too high by two orders of magnitude to explain the measured isotopic compositions the fractionation patterns allow the discrimination between open and closed system behaviour the regional distribution of open and closed system patterns corresponds to the frequency of occurrence of late stage migmatization western part and to differences in amount and composition of fluid inclusions

pedosedimentary and geoarcheological archives from clay dominated sinkhole infillings in middle franconia germany abstract sinkholes in the karstified middle keuper gypsum of middle franconia germany reveal numerous archeological findings and contain unique pedosedimentary records of landscape development and human environment interaction during the holocene mudstone derived high clay contents result in a unique set of sedimentary and pedogenic properties of these archives in that all units exhibit vertic properties since the horizons have a polygenic history detailed field and micromorphological observations together with laboratory analyses grain size color iron pedochemistry are the basis for a classification of the pedosediments 14c dating provides a chronological framework for geomorphological stability phases and thus identified soil forming processes the first anthropogenic colluvial sediments of the studied archive date to the early bronze age and accumulated in an initial karst depression water saturation caused iron reduction of these early infillings in the pedosediments above oxidation and iron release are largely related to changes in the parent material here the soil material contains coarse silt indicating an admixture of nearby periglacial slope deposits furthermore fossil root traces point to a longer time with stable conditions which we interpret as absence of humans or at least an extended period of fallow land the superimposed sediments from the urnfield period are more inhomogeneous and consist of material from the eroded agricultural soils of the surrounding the characteristics of these pedosediments point to intensified human land use pedogenic processes such as iron release reduction of iron swelling shrinking and short distance translocation of clay intensively overprinted all soil sediments in this context micromorphology proved to be an essential tool for the characterization of polygenesis in terms of soil forming as well as redepositional processes that lead to the formation of these complex archives the present study reflects a multi methodological approach to a rather disregarded type of polygenic terrestrial records it constitutes an example for the investigation of clayey pedosediments in karstic environments under moderate climate in the frame of a prehistoric geoarcheological setting

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

oxygen self diffusion in calcite dependence on temperature and water fugacity oxygen self diffusion in natural calcite single crystals was studied hydrothermally at 400 800 c and 10 350 mpa confining pressure diffusion coefficients d were determined from18o concentration profiles measured with an ion microprobe at 100 mpa confining pressure the arrhenius parameters yield an activation energy q 173 6 kj mole and pre exponential factor d0 7 10 9 m2 s over the temperature range 400 800 c and there is no measurable anisotropy constant temperature experiments at 700 c indicate that there is a strong linear correlation slope 0 9 of d with water fugacity over the range 4 240 mpa consistent with the interpretation that in the presence of water the dominant oxygen bearing transport species in calcite is molecular water a sample containing 1180 ppm mn shows a marked increase in observed d values at temperatures below 600 c however when pre annealed at 700 c the d values obtained at 550 c are within a factor of four of the value obtained for the low 100 ppm mn sample the results of this study confirm that in contrast to carbon oxygen diffusion rates in calcite are greatly enhanced when water is present the difference in the effect of water on doxygen and dcarbon in calcite may provide valuable information for evaluating the role of fluids in the thermal histories of calcite bearing rocks

terra rossa genesis implications for karst and eolian dust a geodynamic thread abstract although terra rossa has long been thought to form by residual dissolution of limestone and or by accumulation of detrital mud ash or dust on preexisting karst limestones we present conclusive new field and petrographic evidence that terra rossa forms by replacement of limestone by authigenic clay at a moving metasomatic front several centimeters wide the red clay s major chemical elements al fe and si probably come from dissolved eolian dust the replacement of calcite by clay exhibits a serrated microstylolitic texture that helps prove that replacement happens not by dissolution precipitation as conventional wisdom has it but by pressure solution of calcite driven by the crystallization stress generated by the growth of clay crystals the acid produced by the isovolumetric replacement of limestone by clay quickly dissolves out additional porosity permeability in an adjacent slice of limestone within the front triggering a reactive infiltration instability that should theoretically

clay mineralogy and chemistry of argillic horizons fragipans and paleosol b horizons of soils on a loess thinning transect in southwestern indiana usa abstract in southwestern indiana peorian loess about 20 000 years old thins eastward from the river valleys where it originated and covers sangamon paleosols developed in various parent materials where the loess is thick more than about 2 5 m the entire modern soil profile formed in loess and where it is thin the modern soil and paleosol are contiguous i e welded the objectives of this study were to determine how the mineralogy of the argillic bt horizons of modern soils changes with loess thickness how fragipan horizons bx formed in loess differ from non fragipan horizons formed in loess and how paleosol btb horizons differ from bt horizons and from each other soils were sampled on stable landscape positions along a loess thinning transect about 160 km long free oxides al d fe d si d were extracted with a citrate bicarbonate dithionite solution clay mineralogy was determined qualitatively by x ray diffraction and quantitatively by thermal and chemical methods in the loess derived bt horizons kaolinite content tends to increase and smectite to decrease as loess thins fragipans formed where loess is of intermediate thickness have higher contents of smectite and free silica greater surface area and higher exchangeable mg ca ratios than argillic horizons formed in loess high si d clay and si d fe d ratios are indicators of fragipan development paleosol btb horizons have higher base saturation than modern bt horizons they also contain more kaolinite and less smectite than bt horizons but the paleosols developed in different materials all have similar mineralogy

a new look at stable isotope thermometry interdiffusion between coexisting minerals affects all rocks and causes resetting and discordance of stable isotope geothermometers that is commonly observed in slowly cooled igneous and metamorphic rocks the fast grain boundary fgb model describes the stable isotope fractionations and intracrystalline zonation which result from closed system interdiffusion eiler et al 1991 1992 this model assumes that grain boundary diffusion is much faster than volume diffusion and it accounts for exchange among all minerals in a rock previous models of closure temperature violate mass balance restrictions and will be inaccurate in most rocks modeling results are described for amphibolites and hornblende granites and gneisses biotite granites schists and gneisses pelitic and semi pelitic rocks garnet peridotites anorthosites gabbros pyroxenites and related rocks and calc silicate rocks examples of mineral pairs and specific rock types that allow accurate stable isotope thermometry include plagioclase pyroxene in pyroxene bearing anorthosites and garnet quartz in garnetiferous quartzites in contrast the same mineral pairs in related rocks such as pyroxenites and pelitic schists will exhibit reset apparent temperatures closed system processes are capable of producing a variety of patterns of stable isotope resetting discordance mineral zonation and fractionation reversals examples include large reversals of quartz feldspar fractionations in micaceous rocks and oscillatory zonation in feldspar from some quartz rich rocks these results permit reinterpretation of many studies of stable isotope thermometry speedometry and retrograde alteration history fgb modeling of mineral zonation provides an important new guide to applying recently developed micro analytical tools to slowly cooled rocks application of the fgb model to quartzo feldspathic gneisses from the adirondack mountains new york demonstrates the usefulness of diffusion modeling in discriminating closed system diffusion controlled retrogression from open system retrogression and illustrates the possible importance of incorporating the effect of water activity on mineral diffusivity

pedogenesis of red soils overlaid coral reef terraces in the southern taiwan abstract red soils developed above the reef limestones are commonly observed in the world their characteristic properties of high contents in clays and iron oxides reddish hue are usually classified themselves as inceptisols alfisols ultisols or mollisols in soil taxonomy the genetic contexts between the soils and beneath limestone have been revealed for gauging paleo landform surface processes relating to paleoclimatic shifts since the late pleistocene there are levels of reef marine terraces in altitude in the hengchun peninsula of taiwan their surfaces are covered by thick reddish soil enriched with iron oxides however these terra rossa like soils distributed on the reef limestone are actually developed from heterogeneous detrital materials instead of developing from the insoluble residue of the limestone according to the soil taxonomy the soils on the higher terraces are classified as the typic paleudults or typic kandiultults they are equivalent to the alisols in wrb system the soils on the lower terraces are classified as typic udipsamments and lithic eutrudepts and they are equivalent to the arenosols and cambisols respectively this study suggests that the terra rossa like soils in the study are developed from the parent materials of fluvial deposits which are subject to the landform surface processes during the interglacial

volume self diffusion of oxygen in biotite muscovite and phlogopite micas the kinetics of oxygen self diffusion have been measured in natural samples of biotite muscovite and phlogopite micas under hydrothermal conditions using both bulk exchange and profiling analyses all experiments were run at 1000 bars 100 mpa water pressure except those designed to measure water pressure dependence which ranged from 200 to 2000 bars the arrhenius relations obtained for layer parallel diffusive transport in the three micas by bulk exchange experiments fit to an infinite cylinder model are mineral biotite muscovite phlogopite 34 2 39 5 42 3 9 1 10 6 7 7 10 5 1 4 10 4 t c 500 800 512 700 600 900 the results of ion microprobe sims depth profiling perpendicular to the layers parallel to c axis yield diffusion coefficients 3 to 4 orders of magnitude lower than for transport parallel to the layers a single layer parallel step profiling experiment yields a diffusion coefficient identical within uncertainty to those obtained from bulk exchange experiments a slight dependence of diffusion rate on water pressure may obtain in phlogopite however the difference is approximately within the uncertainty of the measurement diffusion rates are similar within about a half an order of magnitude for a range of biotite composition from annite4 to annite63 as well as for muscovite comparison of oxygen diffusion rates in biotite from this study with ar k and rb diffusion from published data supports the idea that water is the oxygen bearing species in hydrothermal diffusion experiments the implication of these results for natural systems is that the micas especially biotite will continue to exchange oxygen isotopes via volume diffusion down to temperatures as low as 300 c the rapid diffusion kinetics may explain biotite oxygen isotope disequilibrium which is commonly observed even in rocks where other mineral phases preserve equilibrium compositions full size table table options view in workspace download as csv

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

oxygen isotope thermometry using quartz inclusions in garnet oxygen isotope ratios of quartz inclusions within garnet from granulite and amphibolite facies gneisses in the adirondack mountains ny were analyzed and used to determine metamorphic temperatures primary quartz inclusions for eight of 12 samples have 18o values significantly lower than matrix quartz the primary quartz inclusions retain 18o values representative of thermal conditions during garnet crystallization whereas the 18o values of matrix quartz were raised by diffusive exchange with other matrix minerals e g mica and feldspar during cooling the 18o differences between quartz inclusions and matrix quartz show that garnet a mineral with slow diffusion of oxygen can armour quartz inclusions from isotopic exchange with surrounding matrix even during slow cooling these differences between 18o in matrix quartz and quartz inclusions can further be used to test cooling rates by fast grain boundary diffusion modelling criteria for identifying quartz inclusions that preserve primary compositions and are suitable for thermometry were developed based on comparative tests relations between 18o and inclusion size distance of inclusion to host garnet rim core rim zonation of individual inclusions and presence or absence of petrological features healed cracks in quartz inclusions inclusions in contact with garnet cracks lined by secondary minerals and secondary minerals along the inclusion grain boundary were investigated in this study 61 of quartz inclusions preserve primary 18o and 39 were associated with features that were linked to reset 18o values if 18o in garnet is homogeneous and inclusions are removed laser fluorination 18o values of bulk garnet are more precise more accurate and best for thermometry intragrain 18o grt profiles measured in situ by ion microprobe show no 18o zonation almandine rich garnet alm 60 75 from each sample was measured by laser fluorination mass spectrometry lf ms for 18o and compared with ion microprobe measurements of 18o in quartz inclusions for thermometry the 18o qz grt values for adirondack samples range from 2 66 to 3 24 corresponding to temperatures of 640 to 740 c a qz alm 2 71 out of 12 samples that were used for thermometry nine are consistent with previous estimates of peak temperature 625 to 800 c based on petrological and carbon isotope thermometry for regional granulite and upper amphibolite facies metamorphism the three samples that disagree with independent thermometry for peak metamorphism are from the anorthosite mangerite charnockite granite suite in the central adirondacks and yield temperatures of 640 to 665 c approximately 100 c lower than previous estimates these low temperatures could be interpreted as thermal conditions during late post peak crystallization of garnet on the retrograde path this article is protected by copyright all rights reserved

oxygen isotope zoning in garnets from franciscan eclogite blocks evidence for rock buffered fluid interaction in the mantle wedge the oxygen isotope compositions of eclogite and amphibolite garnets from franciscan complex high grade blocks and actinolite rinds encasing the blocks were determined to place constraints on their fluid histories sims oxygen isotope analysis of single garnets from five eclogite blocks from three localities ring mountain mount hamilton and jenner beach shows an abrupt decrease in the 18o value by 1 3 from core to rim at a distance of 120 50 m from the rim in nine out of the 12 garnets analyzed in contrast amphibolite garnets from one block ring mountain analyzed show a gradual increase in 18o value from core to rim implying a different history from that of the eclogite blocks values of 18o in eclogite garnet cores range from 5 7 to 11 6 preserving the composition of the eclogite protolith the abrupt decrease in the 18o values of the garnet rims to values ranging from 3 2 to 11 2 suggests interaction with a lower 18o fluid during the final stages of growth during eclogite facies metamorphism 450 600 c we hypothesize that this fluid is sourced from the serpentinized mantle wedge high mg ni and cr contents of actinolite rinds encasing the blocks also support interaction with ultramafic rock oxygen isotope thermometry using chlorite and phengite versus actinolite of rinds suggests temperatures of 185 240 c at ring mountain and mount hamilton rind formation temperatures together with the lower 18o garnet rims suggest that the blocks were in contact with ultramafic rock from the end of garnet growth through low temperature retrogression we suggest a tectonic model in which oceanic crust is subducted at the initiation of subduction and becomes embedded in the overlying mantle wedge as subduction continues metasomatic exchange between high grade blocks and surrounding ultramafic rock is recorded in low 18o garnet rims and later as temperatures decrease with rind formation

spatial distribution and development of soils in tropical karst areas from the peninsula of yucatan mexico abstract better understanding of soil formation requires knowing the spatial distribution of the soils that allows constructing models of soil sequences in multiple directions along various types of gradients this approach was applied to comprehend the soil formation from the soil distribution in the tropical karst areas of the peninsula of yucatan mexico for soil mapping a two step methodology was followed first a geomorphic analysis was performed subsequently 382 soil profiles were reclassified and integrated into a geopedologic map additional soil survey was carried out in areas where soil information was lacking 123 soil profiles satellite images were used to identify flooded areas after conducting numerous field verifications and analyses landforms and soils were combined to make a soilscape map based on field observations and the soilscape map soil development was analyzed on soil sequences four geomorphic environments were identified karstic plains and hills with leptosols cambisols luvisols and vertisols coastal plains with arenosols regosols solonchacks and histosols fluvio paludal plains with gleysols histosols leptosols and solonchacks and tectono karstic plains and hills with leptosols cambisols luvisols and vertisols relevant soil forming factors in the peninsula of yucatan include time of emersion of the limestone platforms climate rock type and macro and micro relief other factors such as groundwater level fractures also have an influence on soil formation karst development can be considered as a complex soil and relief forming factor terra rossa soils as leptosols cambisols luvisols nitisols and vertisols in the peninsula of yucatan may be polygenic in some cases the theory of residual origin fits better the data than the theory of allochthonous origin in other cases it is the other way around

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

how to overcome imaging problems associated with carbonate minerals on sem based cathodoluminescence systems on sem based cathodoluminescence systems scanned cl methods are needed to overcome image quality problems caused by persistent luminescence of carbonate minerals an effective solution to the persistence problem is to acquire images using only the shorter wavelengths most easily done by using a broadband short wavelength uv blue range filter the filter used provides 80 to 90 transmissivity in the range of 385 to 495 nm and some transmissivity as low as 350 nm the filter allows transmission of the relatively nonpersistent uv violet luminescence present in most carbonates in the range of 350 to 425 nm but blocks the common orange red wavelength luminescence found in carbonates the lack of imaging problems in subsequent images shows that persistent luminescence in carbonates is primarily in the orange red wavelengths cathodoluminescence images produced using a short wavelength filter are comparable in detail to those obtained from conventional light microscope based cathodoluminescence systems in almost all examples features visible in the orange red wavelengths show corresponding variations in luminescence in the shorter wavelengths

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

co evolution of eukaryotes and ocean oxygenation in the neoproterozoic era the oxygenation of the earth s deep oceans is often thought to have triggered the evolution of simple animals a review article proposes that instead the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea

morphology genesis and classification of three soils over limestone jamaica abstract this paper describes three jamaican soils over limestone that are widely different in their genesis morphology and classification following descriptions of the locations of the profiles the environmental conditions governing their formation are discussed two of the profiles are derived from limestone the third is developed in bauxite in all three profiles intense weathering preceded actual soil formation in profiles 1 and 2 weathering of the limestone rock through dissolution of caco3 resulted in the residual accumulation of clay minerals such as kaolinite and chlorite the bauxite deposit in which profile 3 developed represents a very advanced stage of weathering and desilication the origin of the jamaican bauxites is not clear however soil formation in the two soils over limestone an ultisol and an alfisol is characterized by downward movement of clay iron and organic matter and by the formation of an argillic horizon biological mixing oxidation reduction and formation of nodules are additional processes one of these profiles shows a lithological discontinuity in this soil transformation of rock fragments chert into pseudo iron manganese nodules has contributed to soil formation we postulate that the dominant processes in the profile developed in bauxite an oxisol are desilication and residual accumulation of oxides of aluminium and iron into an oxic horizon other soil forming processes in this profile comprise biological activity some iron segregation and nodule formation the three profiles are classified according to the usda soil taxonomy the legend for the fao unesco soil map of the world and the french soil classification system cpcs rationales for placement in these systems are discussed detailed profile descriptions and laboratory data are presented in an appendix

pedogenic carbonate crusts calcretes in karstic landscapes as archives for paleoenvironmental reconstructions a case study from yucatan peninsula mexico abstract in the northeastern margin of the yucatan peninsula which is located in southeastern mexico three levels of compact carbonate crusts calcretes interlayered with indurated coastal calcareous sediments calcarenites are discernible since both the calcretes and calcarenites form a continuous carbonate sequence a combined methodology macro and micromorphology geochemistry and mineralogy is used to differentiate them additionally the calcrete layers are dated using the uranium thorium method in order to establish a chronological framework the carbonate differentiation and chronology are then used to establish the paleoenvironmental conditions that prevailed during calcrete formation as well as to reconstruct the coastal landscape evolution and its relation to pleistocene sea level changes during marine isotope stages mis 6 and 5 samples of calcrete layers and calcarenites were taken from two sections in the cancun tulum corridor the lowest level of calcrete underlies a sequence of calcarenites and the two younger levels cap the sequence in calcretes the micromorphology provides evidence of the presence of a relict soil with subangular blocky microstructure root traces and needle fiber calcite associated with soil fungi interactions in contrast the micromorphology of the calcarenites shows ooids and bioclasts typical of a coastal environment geochemically calcretes are depleted in 13c compared to calcarenite with values ranging between 2 and 10 and they have a lower proportion of rare earth elements calcrete mineralogy consists mainly of calcite over aragonite with a low proportion of mg calcite u th dating indicates that the oldest calcrete was formed during the penultimate glacial maximum pgm in mis 6 and the two younger calcretes correspond to the last interglacial period in mis 5c the calcarenite formation occurred earlier also during mis 5 soil formation strong karstification and soil erosion have occurred on younger calcretes this study suggests that these processes developed between mis 4 to mis 1

geochemical evidence for african dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces northern jamaica west indies abstract the origin of red or reddish brown clay rich terra rossa soils on limestone has been debated for decades a traditional qualitative explanation for their formation has been the accumulation of insoluble residues as the limestone is progressively dissolved over time however this mode of formation often requires unrealistic or impossible amounts of carbonate dissolution therefore where this mechanism is not viable and where local fluvial or colluvial inputs can be ruled out an external source or sources must be involved in soil formation on the north coast of the caribbean island of jamaica we studied a sequence of terra rossa soils developed on emergent limestones thought to be of quaternary age the soils become progressively thicker redder more fe and al rich and si poor with elevation furthermore although kaolinite is found in all the soils the highest and oldest soils also contain boehmite major and trace element geochemistry shows that the host limestones and local igneous rocks are not likely source materials for the soils other trace elements including the rare earth elements ree show that tephra from central american volcanoes is not a likely source either however trace element geochemistry shows that airborne dust from africa plus tephra from the lesser antilles island arc are possible source materials for the clay rich soils a third as yet unidentified source may also contribute to the soils we hypothesize that older more chemically mature jamaican bauxites may have had a similar origin the results add to the growing body of evidence of the importance of multiple parent materials including far traveled dust to soil genesis

increase of seawater mo inventory and ocean oxygenation during the early cambrian abstract the early cambrian radiation of macroscopic animals commonly referred as the cambrian explosion is one of the most important biological innovations in earth history because oxygen is a requirement for complex animal life it is generally accepted that ocean oxygenation may have been the environmental trigger for animal evolution but direct geochemical evidence supporting oxygen increase prior to the cambrian explosion remains sparse and insufficient to better understand the casual relationship between ocean oxygenation and animal evolution we have carried out a systematic analysis of redox sensitive trace element rste concentrations total organic carbon toc contents and pyrite morphology for the early cambrian niutitang formation of the hejiapu section northeastern guizhou province south china the new data in combination with previously published data from other sections show strong mo enrichments average of 88 ppm and high mo toc ratios average of 14 ppm wt in the euxinic black shales of the lower niutitang formation 520 ma indicating increase of the oceanic mo reservoir in the light of the positive correlation between sediment mo toc and aqueous mo in modern basins the early cambrian oceanic mo concentration is estimated as 50 nmol which is about half of the modern ocean mo concentration 105 nmol but is significantly higher than that of the mesoproterozoic oceans 10 20 nmol the marked increase in oceanic mo reservoir is therefore interpreted as recording significant rise of atmospheric oxygen and pervasive ocean oxygenation which may have facilitated the diversification of macroscopic metazoans during the early cambrian

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

an emp and tem aem study of margarite muscovite and paragonite in polymetamorphic metabauxites of naxos cyclades greece and the implications of fine scale mica interlayering and multiple mica generations