sr isotope stratigraphy assigning time in the campanian pliensbachian toarcian and valanginian abstractthe trend of marine 87sr 86sr against stratigraphic level through sections whether linear or not can identify hiatuses and changing rates of sedimentation through those sections and so be a valuable constraint on attempts to assign numerical ages to sediments on the basis of astrochronology or u pb dating of zircons here we illustrate that value for the campanian pliensbachian toarcian and valanginian ages by comparing 87sr 86sr profiles for different localities and comparing those to the 87sr 86sr profile through time the analysis reveals possible problems both with current time scales and with some astrochronological calibrations our analysis is neither comprehensive nor final rather with a few examples we show how sr isotope stratigraphy can be used to moderate other methods of assigning numerical ages to sediments

dendritic calcite crystals formed by calcification of algal filaments in a vadose environment abstract uncalcified and calcified algae grow on and color walls of cavities that occur in karst breccia which fills pockets in the tertiary bluff formation of grand cayman island the calcified algae are important because the calcification has been achieved through the formation of dendritic calcite crystals although common in metals such branching crystals have not been widely recognized in naturally occurring calcite the dendritic calcite crystals are exactly like most dendritic crystals in that they have a primary needle or stem with secondary and tertiary branches most dendritic calcite crystals have an open treelike form and are easy to recognize as calcification proceeds the dendritic crystals become progressively filled in and are increasingly difficult to recognize as dendritic crystals filling of the dendritic crystals can result in two dimensional sheets or three dimensional columns assuming the three dimensional columnar dendritic crystals developed planar and or curving smooth surfaces then lacking other evidence they would be indistinguishable from normal columnar calcite crystals and their dendritic origin would be hidden variables thought to control dendrite crystal formation include a creation of localized highly supersaturated solutions leading to rapid rates of nucleation and crystal growth and b impurities in the form of organic molecules and other substances algae are excellent candidates for controlling a via their metabolism and contributing to b via their decay combining these ideas with the results of this study and with the known common occurrence of algae in many speleothemic environments provides an impetus for a reexamination of the origin of subaerially formed calcite crystals

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

tourmaline kar ages compared to other radiometric dating systems in alpine anatectic leucosomes and metamorphic rocks cyclades and southern spain abstract k ar ages of tourmalines from alpine anatectic leucocratic rocks in the migmatite dome on naxos greek cyclades and along ultramafic intrusions in southern spain are older than the corresponding mineral ages they are interpreted as cooling ages closely approaching the age of magmatism suggesting a closure temperature exceeding that of hornblende rb sr whole rock analyses from metagranites and gneisses of the palaeozoic suite of the mulhacen complex of the betic cordilleras southern spain yield errorchrons of between 275 and 191 ma several k ar tourmaline ages of these rock units are higher than the corresponding whole rock ages pointing to the incorporation of excess radiogenic ar of the young tourmalines three of them give ages of 80 85 ma indicating possible examples of incomplete degassing and or possible incorporation of excess radiogenic ar in the mineral during the alpine metamorphism the tourmaline ages are compared with the ages of the coexisting micas these have a range of k ar ages consistently higher than the corresponding young alpine rb sr ages of 15 6 12 5 ma pointing to a complex behavior for radiogenic ar during the alpine metamorphism

genesis and microstratigraphy of calcite coralloids analysed by high resolution imaging and petrography abstract the genesis of calcite coralloid speleothems from lamalunga cave southern italy is here investigated from a purely petrographic perspective which constitutes the basis for any subsequent chemical investigation lamalunga cave coralloids formed on bones and debris on the floor of the cave they consist of elongated columnar crystals whose elongation progressively increases from the flanks to the tips of the coralloid forming a succession of lens shaped layers which may be separated by micrite or impurity rich layers organic molecules are preferentially concentrated toward the centre of convex lenses as highlighted by epifluorescence their occurrence on cave floor lens shaped morphology and concentration of impurities toward the apex of the convex lenses supports the hypothesis that their water supply was hydroaerosol generated by the fragmentation of cave drips evaporation and degassing preferentially occurred on tips enhancing the digitated morphology and trapping the organic molecules and impurities carried by the hydroaerosol between the growing crystals which became more elongated micrite layers that cap some coralloid lenses likely identify periods when decreasing in hydroaerosol resulted in stronger evaporation and higher supersaturation with respect to calcite of the parent film of fluid this interpretation of coralloid formation implies that these speleothems can be used to extract hydroclimate information

sedimentology and geochemistry of a human induced tufa deposit implications for palaeoclimatic research geochemical variations across laminated tufas and travertines may reflect the growth style of the carbonate build up and not just climate related changes this work presents the study of a carbonate deposit formed on a ravine wall in gran canaria island spain from a broken pipe system used for irrigation of banana plantations the deposit is a few tens of metres long and has a stepped morphology formed by successive cascade barriers and pools the main facies are framestones of coated stems laminated bindstones phytoclastic wackestones and silty mudstones all of which display micritic or coarse crystalline textures lamination from a framestone with coarse crystalline texture was studied from a petrological sedimentological and geochemical perspective and water palaeotemperatures were calculated lamination displaying five orders of magnitude from daily to annual or higher was controlled by the discontinuous supply of water lamination consists of crystalline laminae discontinuity couplets at all observed scales estimated mean precipitation rates are 0 7 mm year 1 but discontinuity of sedimentation at all lamination orders may have involved greater precipitation rates whereas elemental geochemistry suggests variable conditions not far from chemical equilibrium stable isotopes suggest that calcite precipitated under disequilibrium conditions however the small dimensions of the deposit and the relatively high flow velocities allowed lack of 13c and 18o isotope fractionation in co2 nor in calcite leading to independent temperature calculations both with mean values of 25 c isotopic trends found throughout lamination cannot be explained by strong changes in water temperature nor in 13cdic or 18ow the correction made to eliminate these isotopic trends yielded narrower temperature ranges this paper discusses the accuracy of temperature estimations despite the difficulties coming from disequilibrium and how isotopic trends through time could be explained by the growth of the deposit and not by climate related changes

step leach pb pb dating of inclusion bearing garnet and staurolite with implications for early proterozoic tectonism in the black hills collisional orogen south dakota united states we report 207 pb 206 pb stepwise leaching pbsl ages of 1762 15 ma 1759 8 ma and 1760 7 ma for almandine garnet staurolite and garnet staurolite combined in an early proterozoic metapelite from the black hills collisional orogen south dakota pbsl derived 208 pb 206 pb th u trends reveal that staurolite contains inclusions of both cogenetic monazite ca 1760 7 ma and older detrital zircon 2040 ma whereas coexisting garnet contains only the zircon these results and petrologic data indicate prograde sequential growth of garnet monazite and staurolite during tectonic burial at temperatures between 400 c and 550 c i e well below pb closure temperatures we interpret the 1760 7 ma date as a maximum age for wyoming superior continental collision in the black hills which apparently postdated the 1800 1900 ma trans hudson orogeny in canada but was nearly synchronous with north directed accretion of the central plains orogen in southeastern wyoming

astronomical duration of polarity chron c31r lower maastrichtian cyclostratigraphy of odp site 762 indian ocean and the contessa highway section gubbio italy the duration of polarity chron c31r is estimated with a cyclostratigraphic approach two sites are investigated odp site 762 indian ocean and the contessa highway section gubbio italy cyclostratigraphic analysis is performed on greyscale variations site 762 and magnetic susceptibility variations contessa section both sites reveal an astronomical control of the sedimentation highlighted by the identification of all the orbital periodicities cyclostratigraphic signals are tuned on 405 ka eccentricity cycles extracted from the la04 astronomical solution in both sites cycle counting gives an estimate of the duration of polarity chron c31r of about 2 09 0 03 ma

special speleothems in cement grouting tunnels and their implications of the atmospheric co2 sink based on the analyses and comparisons of water chemistry stable carbon isotopes and deposition rates of speleothems the authors found that there are two kinds of speleothems in the tunnels at the wujiangdu dam site guizhou china namely the co2 outgassing type and the co2 absorbing type the former is natural as observed in general karst caves and the product of karst processes under natural conditions the latter however is special resulting from the carbonation of a cement grouting curtain and concrete due to the quick absorption of co2 from the surrounding atmosphere evidenced by the low co2 content in the air and the high deposition rate of speleothems as high as 10 cm a in the tunnels the contribution of the carbonation process to the sink of co2 in the atmosphere is important in the order of magnitude of 108 tons c a and should be taken into consideration in the study of the global carbon cycle because of the use of cement on a worldwide scale

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

biogenic structures and micrite in stalactites from grand cayman island british west indies stalactites from modern and old caves developed in the bluff formation of grand cayman island contain laminae and bulbous masses of micrite intercalated with sparry calcite the micrite as well as some of the sparry calcite around it contains small up to 25 m long ovate to spherical bodies that have a high concentration of either manganese or iron such bodies may be of bacterial origin the micrite contains numerous calcified filaments that are probably of algal origin calcification of the filaments occurred either during life or shortly after death of the algae the algae played an important role in trapping and binding the micrite furthermore the algae may be directly or indirectly responsible for the formation of much of the micrite

campanian paleoseismites of the elk basin anticline northern bighorn basin u s a a record of initial laramide deformation abstract paleoseismites in the form of clastic dikes and sills and convolute bedding record syndepositional tectonism prior to lithification fold growth and onset of major orogenic events the elk basin anticline located in the northern portion of the bighorn basin contains paleoseismites in campanian strata along its eastern forelimb and western back limb margins in the shallow marine telegraph creek and claggett formations convolute bedding typically involves individual sandstone beds with vertical to overturned strata on either side of a nearly vertical vent whereas the nonmarine eagle formation contains planar clastic dikes and sills derived from liquefied sand source beds and convoluted bedding involving distorted laminae planar clastic dikes and sills were injected upward and laterally across overlying strata and along pre existing nearly vertical near surface joints geographically clastic dikes and sills are present only in the central portion of the anticline while convoluted bedding is present in the central and southern portions comparison of 145 clastic dike measurements with 61 previously reported laramide joint set orientations for the elk basin demonstrate trends to be similar clastic dikes preferentially fill cross joints oriented normal to the axial trace of the anticline while strike joints illustrate a dominant later laramide joint set oriented subparallel to the axial trace paleoseismite formation is consistent with m 5 5 earthquakes during earliest laramide deformation associated with development of the elk basin thrust fault whereas strike joints formed during subsequent laramide deformation after burial and cementation of campanian strata

strengthening the link between geochronology textures and petrology time must be integrated with other geologic parameters such as pressure temperature p t composition or structural textural information in order to quantify the dynamics of geologic processes like mountain building faulting metamorphism or magmatism in the past this connection was weak due to large sample sizes required in geochronology however recent developments open up exciting new possibilities texturally controlled in situ dating of minerals utilizing uv laser ablation 40ar 39ar or rb sr microsampling facilitates the crucial link between ages and textures at high spatial resolution in situ u pb ages of accessory minerals can now be linked to the corresponding p t evolution via their characteristic trace elemental signatures indicative of mineral reactions in rocks garnet dating by sm nd and more recently lu hf can greatly benefit from both laser ablation inductively coupled plasma mass spectrometry icpms screening and improved leaching strategies improving the link between time and p t such integrated approaches can yield the duration and rates of deformation in shear zones the rates of burial and exhumation of subducted rocks or the duration of entire metamorphic loops to name a few potential for further development is identified in diverse areas dating of carbonate minerals related to brittle faulting using u pb could provide previously unavailable constraints on rates and duration of brittle deformation in the earth s upper crust in situ rb sr dating applicable to micas could become available using either laser ablation dynamic reaction cell icpms or microbeam accelerator mass spectrometry other future developments and trends and their limitations are discussed briefly

the role of inclusions in u pb and sm nd garnet geochronology stepwise dissolution experiments and trace uranium mapping by fission track analysis the u pb and sm nd dating of garnet are important tools for understanding rates of tectonometamorphic processes and have been widely applied in studies of metamorphic terranes however the budgets of uranium lead samarium and neodymium in garnet separates from metamorphic rocks may be dominated by contributions from inclusions of monazite or zircon a combined fission track and stepwise dissolution technique is proposed for evaluating the role of inclusions of monazite and zircon in the budgets of uranium lead samarium and neodymium in garnets used for u pb and sm nd chronology variations of th u u nd and sm nd ratios between successive dissolution steps reveal the contributions of monazite and zircon inclusions the stepwise dissolution procedure does not induce any apparent artifacts on 207pb 206pb and sm nd ages the technique has been applied to garnets from three metamorphic terranes almandine garnet samples from the high grade pikwitonei granulite domain manitoba canada and the wind river range wyoming usa have the majority of their uranium samarium neodymium and radiogenic lead pb hosted by micrometer scale inclusions of monazite fission track densities reveal that uranium is 108 times more abundant in inclusions than in garnets stepwise dissolution of the samples shows that neodymium and uranium are associated with the dissolution of monazite in contrast grossularandradite garnets from cascade slide adirondack highlands ny usa show little variation in fission track density and similar isotopic ratios between dissolution steps indicating that the budgets of uranium samarium neodymium and pb are not significantly influenced by inclusions the demonstrated success of these techniques leads us to recommend similar procedures as a routine matter in u pb and sm nd garnet geochronology of metasedimentary rocks

an assessment of the utility of staurolite in u pb dating of metamorphism pb isotope data major and trace element compositions fission track and synchrotron x ray fluorescence analyses are presented for staurolites from nine pelitic schists in the continental united states to evaluate their potential use in u pb geochronology seven u pb analyses from lanzirotti and hanson 1995 are reexamined with respect to this additional data which was not available at the time these data are then compared to 21 new u pb analyses of staurolite of varying composition from a variety of localities the primary goals of this study are to 1 evaluate the variability in u and pb abundance and u pb ratio in staurolites of varying composition 2 constrain how much of the measured u and pb is derived from radiogenic solid inclusions such as monazite and zircon 3 constrain how much of the measured u and pb is derived from staurolite itself and evaluate any possible correlation of u and pb abundance and u pb ratio to major element composition 4 place preliminary constraints on closure temperature to pb diffusion in staurolite 5 evaluate how meaningful u pb ages can better be calculated for the low u pb ratio minerals in the staurolite fractions analyzed u abundances range from 0 2 to 24 9 ppm pb from 0 13 to 2 41 ppm the 238u 204pb ratios vary from 135 to 9447 and the 206pb 204pb ratios from 23 to 623 for many of the fractions analyzed precise u pb ages can be calculated 10 ma or better that appear to be consistent with available age constraints on the time of peak metamorphism mass balance calculations fission track analysis and synchrotron x ray fluorescence trace element mapping show that although radiogenic inclusions are almost always present in large staurolite porphyroblasts it is difficult for inclusions to account for the measured pb isotopic compositions it is also demonstrated that the u pb ages calculated for staurolites from connecticut are at least 20 ma older than nearby rb sr muscovite and 40ar 39ar hornblende ages this is consistent with staurolite having a closure temperature to u and pb diffusion significantly higher than 500 c

post orogenic 1500 ma thermal history of the proterozoic eastern fold belt mount isa inlier australia the paucity of sedimentary rocks younger than 1500 ma within the mt isa inlier renders it difficult to determine its post orogenic exhumation and tectonic history except by inference from the stratigraphy of the surrounding areas we present hornblende white mica biotite and alkali feldspar 40ar 39ar data from the eastern fold belt of the inlier which reveal a previously unrecognised complex post orogenic non linear cooling history plateau and total fusion 40ar 39ar ages range between 1500 and 1130 ma and record increases in regional cooling rates of up to 18 c my during 1460 1410 and 1280 1050 ma forward modelling of the alkali feldspar 40ar 39ar arrhenius parameters reveals subsequent increases in cooling rates during 740 640 and 600 500 ma the cooling episodes were driven by both erosional exhumation at maximum rates of 0 9 km my and thermal relaxation following magmatic events early mesoproterozoic cooling is synchronous with exhumation and shearing during the anmatjira event in the arunta block and late mesoproterozoic cooling occurred at the same time as magmatic events in the arunta and musgrave blocks as well as grenville aged orogenesis in the albany fraser belt more localised cooling during the middle neoproterozoic may be a far field response to the separation of australia and laurentia whereas latest neoproterozoic cambrian cooling and exhumation was probably driven by collisional tectonics associated with the petermann ranges and delamerian orogenic events major changes in the stress field of the australian plate that are synchronous with the assembly and break up of rodinia and gondwana resulted in the repeated brittle reactivation of the eastern fold belt probably via the displacement of long lived basement faults

recalibration of the geomagnetic polarity timescale the quest for improved time control to estimate rates of geologic and paleoenvironmental processes is central to the earth sciences until the middle of this century geochronology was based solely on macrofossil evolution providing the largely unmodified definition of geologic stages in the last few decades with impetus from the deep sea drilling project dsdp and the ocean drilling program odp microfossil biostratigraphy has become increasingly important although new radiometric techniques have resulted in improved absolute age precision the direct correlation of absolute ages to biozonations and hence to geologic stage boundaries remains poor this is due to the difficulty of finding materials suitable for radiometric dating which can be directly correlated to biozonations the bridge between biozonations and absolute ages and the interpolation between absolute ages are best accomplished particularly for cenozoic and late mesozoic time through the geomagnetic polarity timescale gpts the template for late jurassic to quaternary geomagnetic polarity is derived from oceanic magnetic anomalies as demonstrated by heirtzler et al 1968 the gpts can be constructed using oceanic magnetic anomaly record s assuming constant seafloor spreading rate s and interpolating between available radiometric ages in the last quadrennium there have been outstanding developments in radiometric dating and astrochronology which have greatly improved the absolute age control of the gpts

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

a crystal chemical basis for pb retention and fission track annealing systematics in u bearing minerals with implications for geochronology this study develops an empirical crystal chemical framework for systematizing the kinetics of pb loss and fission track annealing in u bearing minerals ionic porosity z the fraction of a mineral s unit cell volume not occupied by ions potentially accounts for kinetic behavior by monitoring mean metal oxygen bond length strength various tests of a general kinetics porosity relationship are presented based upon diverse mineral data including 1 pb diffusion parameters 2 measured closure temperatures tc for fission track annealing and 3 retentivities of both pb and fission tracks from apparent age data every kinetic parameter including tc and mineral age for both the u pb and fission track systems is inversely correlated with z within the sub assemblage zircon z 29 titanite 34 and apatite 38 assuming a diffusional closure model pb isotopic transport phenomena are described by a tc z scale calibrated with field based tc data for titanite 680 20 c and apatite 500 c extrapolation of this scale yields tc estimates for the following minerals staurolite tc 1060 c z 25 garnet 1010 c 26 5 zircon 900 c monazite xenotime and epidote 750 c 32 and ca clinopyroxene 670 30 c 34 1 depending on composition these empirical results imply that a u pb pb date for staurolite or garnet records the time of mineral growth not post growth isotopic closure as also concluded in recent field studies because z systematizes fission track annealing this recrystallization process like volume diffusion must also be rate limited by the strength of chemical bonds the extent to which other recrystallization processes are likewise rate limited is important to u pb geochronology because they potentially compete with diffusion as mechanisms for pb isotopic resetting in nature

the azuaje travertine an example of aragonite deposition in a recent volcanic setting n gran canaria island spain the azuaje travertines in the north of gran canary island crop out in the azuaje gorge which is incised into miocene volcanic breccias of the roque nublo formation this travertine is interesting because of the scarcity of travertines in the canary islands and its close relationship with recent volcanic events part of the travertine overlies a lava flow dated at 2420 40 years bp the travertine is composed mainly of aragonite in both perched systems on the gorge walls and in gorge bottom deposits parallel to the present stream perched systems include deposits from the feeder conduits within the roque nublo formation that spilled out through waterfalls and over barriers the gorge valley bottom system includes barrier and pool deposits the main laminated facies are composed mostly of large fibrous aragonite crystals while there are also common micritic and porous microfabrics shrubs coated grains coated bubbles and rafts are present in many of the deposits detailed study of the microfacies shows the presence of sparsely distributed biogenic features the 13c values are between 4 0 and 11 0 and the 18o values range between 11 0 and 2 0 vpdb these 13c values lie within the range of those of thermogene travertines fed by thermal waters that cooled downstream as indicated by the increase of the carbon and oxygen isotope values in that direction the common occurrence of fibrous radial fabrics is interpreted to be due to disequilibrium conditions during aragonite precipitation disequilibrium was likely caused by rapid co2 degassing of the thermalwaters that led to a rapid increase in the degree of aragonite saturation thus themorphology of the aragonite crystals and the isotopic composition indicate that the formation of the azuaje travertine was mostly due to abiogenic processes induced by rapid degassing of thermalwaters linked to the presence of a recent lava flow within the gorge in short the azuaje travertine shows the important role of volcanic activity in travertine deposition in the facies distribution as well as in the geochemical signatures of the deposits and so can be used as a recent analogue for ancient travertine deposits in volcanic settings

geochronological constraints on tourmaline formation in the western fold belt of the mount isa inlier australia evidence for large scale metamorphism at 1 57 ga boron metasomatism during two deformational events resulted in tourmaline formation in parts of late palaeoproterozoic eastern creek volcanics of the western fold belt of the mount isa inlier despite low u pb ratios 1 as measured by laser ablation icp ms when the step leaching process was applied to the tourmaline it process extracted pb fractions with 206 pb 204 pb up to 76 illustrating the method s ability to efficiently separate radiogenic and common pb that are hosted in different crystal lattice sites tourmaline from two syn d2 metamorphic hydrothermal veins at anderson s lode and eldorado yield similar pb step leaching ages of 1573 12 and 1577 48 ma respectively tourmaline from a post d2 but pre d3a vein at king was dated at 1528 51 ma although there is evidence to suggest some contribution from u rich inclusions i e zircon and monazite to some leach steps the isochrons are thought to provide robust ages for hydrothermal tourmaline formation during two discrete thermal events this is supported by estimates of pb closure temperatures in tourmaline derived from ionic porosity models the 1575 ma ages for d2 also reflect the main metamorphic event in the western fold belt but are 40 myr older than accepted age estimates for this episode the revised timing for peak metamorphism tectonism in the western fold belt corresponds with the age of metamorphism in the eastern fold belt suggesting broadly coeval tectonic histories across the entire inlier from at least 1600 ma

tectonic stratigraphic and sedimentologic significance of a regional discontinuity in the upper judith river group belly river wedge of southern alberta saskatchewan and northern montana the lithostratigraphic interval between the taber and lethbridge coal zones in the upper portion of the nonmarine judith river group of southeastern alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity the lower unit referred to here as the oldman formation is characterized by very fine grained to fine grained sandstones that contain fewer than 2 volcanic rock fragments sandstone bodies with numerous sets of horizontally stratified sandstone showing little or no evidence of lateral accretion siliceous paleosols ganisters and a relatively high gamma ray signal in the upper half of the formation the oldman formation comprises deposits of a low sinuosity perhaps ephemeral fluvial system that originated in the southern cordillera of canada and northern montana and flowed northeastward perpendicular to the axis of the alberta basin the upper unit is assigned to a new formation the dinosaur park formation and is characterized by

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

petrology geochronology and isotope geochemistry of the post 1820 ma granites of the mount isa inlier mechanisms for the generation of proterozoic anorogenic granites four distinct episodes of granitic intrusion occurred in the mount isa inlier at 1820 1800 ma 1760 1740 ma 1700 1670 ma and 1560 1480 ma combined these granites cover at least 4700 km2 and they contrast in composition and intrusive style with an earlier major felsic magmatic event which occurred between 1870 and 1840 ma post 1820 ma granite batholiths are of two types large major coarse grained anorogenic i type intrusives and small minor microgranites which are probably s type the i type granites are all pink to red colour and most contain fluorite rapakivi textures are common they have a high ratio of fe mg and are more enriched in tio2 zr nb y and u than the 1870 1840 ma felsic igneous rocks the post 1820 ma i types are interpreted to have formed by small degrees of partial melting of a mafic underplate the smaller microgranites are relatively k2o enriched and are sometimes muscovite bearing they are interpreted to be derived from proterozoic feldspathic metasediments the first three episodes of granite magmatism are coeval with major extensional sedimentary sequences but they are generally spatially displaced from the maximum area of surface rift development this separation is predicted by the asymmetric detachment model of continental extension the tectonic relationship of the youngest granite episode is not clearly defined the 143nd 144nd initial ratios of the post 1820 ma granites fall into two groups one having positive relatively primitive nd values of 1 8 to 3 5 the other having negative nd values ranging from 2 9 to 3 7 samples with positive nd values are interpreted as partial melts of mafic sources formed post 1870 ma whilst the group with negative nd values are derived from significantly older sources formed probably around 2300 2000 ma the sources of these granites are produced by significant underplating events that may occur during either extension or compression

the timing of high temperature retrogression in the reynolds range central australia constraints from garnet and epidote pb pb dating lower calcsilicate unit metasediments and underlying migmatitic napperby gneiss metagranite at conical hill in the reynolds range central australia underwent regional high grade 680 to 720 c low pressure high temperature metamorphism at 1594 6 ma the lower calcsilicate unit is extensively quartz veined and epidotised and discordant grandite garnet epidote quartz veins may be traced over tens of metres depth into pegmatites that pooled at the lower calcsilicate unit napperby gneiss contact the quartz veins were probably precipitated by water rich fluids that exsolved from partial melts derived from the napperby gneiss during cooling from the peak of regional metamorphism to the wet granite solidus pb stepwise leaching pbsl on garnet from three discordant quartz veins yielded comparable single mineral isochrons of 1566 32 ma 1576 3 ma and 1577 5 ma which are interpreted as the age of garnet growth in the veins these dates are in good agreement with previous sensitive high resolution ion microprobe shrimp ages of zircon and monazite formed during high temperature retrogression 1586 5 to 1568 4 ma elsewhere in the reynolds range the relatively small age difference between peak metamorphism and retrograde veining suggests that partial melting and melt crystallisation controlled fluid recycling in the high grade rocks however pbsl experiments on epidote intergrown with and partially replacing garnet in two of the veins yielded isochrons of 1454 34 and 1469 26 ma the 100 120 ma age difference between intergrown garnet and late epidote from the same vein suggests that the vein systems may have experienced multiple episodes of fluid flow

stable isotope data as constraints on models for the origin of coralloid and massive speleothems the interplay of substrate water supply degassing and evaporation abstract many speleothems can be assigned to one of two morphological groups massive speleothems which consist of compact bulks of material and coralloids which are domal to digitate in form faster growth on protrusions of the substrate occurs in the typical growth layers of coralloids where those layers are termed coralloid accretions but it is not observed in the typical layers of massive speleothems which in contrast tend to smoothen the speleothem surface and can therefore be defined as smoothing accretions the different growth rates on different areas of the substrate are explainable by various mechanisms of caco3 deposition e g differential aerosol deposition differential co2 and or h2o loss from a capillary film of solution deposition in subaqueous environments to identify the causes of formation of coralloids rather than massive speleothems this article provides data about 13c and 18o at coeval points of both smoothing and coralloid accretions examining the relationship between isotopic composition and the substrate morphology in subaerial speleothems data show enrichment in heavy isotopes both along the direction of water flow and toward the protrusions the first effect is due to h2o evaporation and co2 degassing during a gravity driven flow of water gravity stage and is observed in smoothing accretions the second effect is due to evaporation and degassing during water movement by capillary action from recesses to prominences capillary stage and is observed in subaerial coralloids both effects coexist in smoothing accretions interspersed among coralloid ones intermediate stage thus this study supports the origin of subaerial coralloids from dominantly capillary water and disproves their origin by deposition of aerosol from the cave air on the other hand subaqueous coralloids seem to form by a differential mass transfer from a still bulk of water toward different zones of the substrate along diffusion flux vectors of nutrients perpendicular to the iso depleted surfaces finally this isotopic method has proved useful to investigate the controls on speleothem morphology and to obtain additional insights on the evolution of aqueous solutions inside caves

microprobe monazite geochronology putting absolute time into microstructural analysis abstract high resolution compositional mapping and dating of monazite on the electron microprobe is a powerful addition to microstructural analysis and an increasingly important tool for tectonic analysis microprobe monazite geochronology can be an efficient reconnaissance tool for evaluating metamorphic and deformational age domains but more importantly its in situ nature and high spatial resolution offer an entirely new level of structurally and texturally specific geochronologic data that can be used to put absolute time constraints on p t d paths constrain the rates of metamorphic and deformational processes and provide new links between metamorphism and deformation microprobe geochronology is particularly applicable to three persistent microstructural microtextural problem areas 1 constraining the chronology of metamorphic assemblages 2 constraining the timing of deformational fabrics and 3 interpreting other geochronological results although some monazite generations can be directly tied to metamorphism or deformation at present the most common constraints rely on monazite inclusion relations in porphyroblasts that in turn can be tied to the deformation and or metamorphic history microprobe mapping and dating allow geochronology to be incorporated into the routine microstructural analytical process resulting in a new level of integration of time t into p t d histories

mineralogical footprints of microbial life earth s geosphere is intimately tied to its biosphere a major link between the two lies in the microbial realm microorganisms grow in and upon rocks and minerals often relying on their substratum for critical compounds needed in order to produce cellular energy the presence of a metabolizing cell on a mineral substrate has a significant effect on the mineral texture and on the geochemistry of the surrounding microenvironment in nature microorganisms exist in microbial commu nities as mats or biofilms growing upon a solid substrate as such they cover a vast surface area both within and below the surface of earth s land and sea the following review will provide a glimpse into the latest findings in the field of geomicrobiology and is intended to convey a sense of the profound influence microorganisms can have upon the geological environment they inhabit

magnetostratigraphy of upper cretaceous strata of the sacramento valley california a magnetic polarity zonation has been developed for nine stratigraphic sections of the upper cretaceous portion of the great valley group in the sacramento valley of california collectively the sections include five biostratigraphic range zones based on ammonites and other mollusks the zones are all of santonian or campanian age and each section contains at least two zones a total of 681 fully oriented samples was collected from 252 horizons spanning more than 3 km of section the samples were subjected to alternating field demagnetization after it was found that the rocks were not amenable to thermal demagnetization rock magnetic studies were used to determine that the principal magnetic carrier is magnetite the paleomagnetic measurements reveal the existence of an interval of reversed polarity that is consistently associated with one of the zones namely the baculites chicoensis zone given the biostratigraphic control the reversed interval can be unambiguously correlated with the first reversed interval following the cretaceous long normal interval on the magnetic polarity time scale this reversed interval corresponds to marine magnetic anomaly 33r the correlation of the re versed interval implies that the base of the chicoensis zone is nearly coincident with the santonian campanian boundary in california and that it is not significantly time transgressive between the shallow water facies on the east side of the sacramento valley and the deep water facies on the west side furthermore the magnetostratigraphy supports the conclusion that all of the zones underlying the chicoensis zone are pre campanian in age a result which is consistent with other lines of evidence the biostratigraphy of these sections in california can now be compared directly to that of the paleomagnetic stratotype section in gubbio italy

cave minerals of the world 2nd edition by carol hill and paolo forti national speleological society huntsville al 463 p isbn number 1 879961 07 5 70 00 think about all of those spectacular displays of mineral crystals that grace the world s mineral museums a great many of the large faceted crystals grew in some sort of cavity over long periods of time such mineral crystals are discovered in vugs pockets and cavities exposed in mines and quarries the conditions under which they were found are very different from the conditions under which they grew the fluids from which they grew are long gone a challenge for mineralogists to deduce from the surviving clues of trace elements isotopes and fluid inclusions now consider a cave it also is a cavity maintaining conditions of constant temperature water vapor pressure and carbon dioxide pressure for long periods of time this is also an environment where minerals can grow but in the case of many caves human observers can watch the growth process in progress some cave minerals appear as large faceted crystals some are nondescript crusts of little beauty but fascinating mineralogy most have formed from flowing dripping and seeping water and thus take on shapes dictated by the idiosyncrasies of the moving water such mineral deposits are known as speleothems stalactites stalagmites flowstone and a host of more intricate shapes hill and forti illustrate speleothems with some spectacular color photographs the authors have solicited contributions from cave photographers all over the world and without exception the

bentonite chemical features as proxy of late cretaceous provenance changes a case study from the western interior basin of canada abstract bentonite beds are fairly common in both marine and terrestrial upper cretaceous campanian maastrichtian deposits of the western interior basin of western canada and northwestern united states a detailed stratigraphic sedimentologic geochemical x ray fluorescence and mineralogical x ray diffraction study of twenty one bentonites from the puskwaskau and wapiti formations in the grande prairie area west central alberta canada is here presented major and trace element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products resulted from intense volcanic arc to within plate pyroclastic activity concentration values of high field strength elements hfse and selected large ion lithophile elements lile e g nb zr th and y obtained by x ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition a comparative analysis of geochemical compositions between grande prairie bentonites and 30 known volcanic beds from central and southern alberta manitoba and montana 1 documents a trend toward more acidic and alkali depleted volcanic products during the late campanian early maastrichtian interval and 2 suggests a well constrained stratigraphic and geographic subdivision of the non marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds furthermore geochemical fingerprints of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds this multiple approach provides a reliable tool for basin scale identification and correlation of non marine sedimentary successions

single mineral pbpb dating a new stepwise leaching procedure applied to ca bearing silicates enables the selective recovery of radiogenic and common pb from a mineral and thus makes single phase pbpb dating possible this permits independent dating of rock forming minerals within a paragenetic sequence and the direct combination of age data with petrological results furthermore the stepwise leaching technique has the advantage over multi phase pbpb dating in that it does not require initial pb isotope equilibrium among the phases but may be used to test it the presence of microscopic solid inclusions which complicate dating of single phases if they are not in equilibrium with the host can be traced via the behaviour of the 208pb 204pb ratio through the various leaching steps this constitutes a major advantage over conventional bulk phase pbpb dating in addition the precision of an isochron age can be improved relative to that of the bulk mineral approach since the 207pb 204pb and 206pb 204pb data spread is significantly enhanced therefore the technique may both be used to date younger phases and or minerals with less favourable u pb ratios and to extend the applicability of self consistent p t t modelling

chronology of magmatism skarn formation and uranium mineralization mary kathleen queensland australia uranium mineralization is hosted in a metasedimentary sequence intruded by felsic and mafic bodies in which the zircon u pb systems are 1 730 to 1 740 m y old felsic dikes characterized by exceptionally high uranium contents crystallized at essentially the same time 1 737 or 15 m y primary rb sr systematics in these igneous rocks are profoundly disturbed u pb discordia establish age of uranium mineralization as 1 550 or 15 m y derivation of uranium protore in the host rocks prior to regional metamorphism and 1 550 m y uraninite formation was probably by ca 1 740 m y hydrothermal activity modified journal abstract

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

shrub morpho types as indicator for the water flow energy tivoli travertine case central italy abstract travertines from tivoli area central italy possess abundant shrub like fabrics that are laterally continuous over hundreds of square meters they occur dominantly in horizontal layers with aggradational and progradational stacking patterns their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the pre salt reservoirs offshore brazil and angola with huge oil accumulations petrographic and micro computer tomography analyses allowed the identification of six shrub morpho types i e narrow dendriform wide dendriform fili dendriform arborescent arbustiform and pustular dendriform shrubs are the most common lithotype in tivoli area and three different subtypes could be distinguished according to the arrangement of their branches the shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite ranging in average from 1 to 3 cm in height the shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas changing laterally into a slope system with crusts as the main lithotype changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho types making them very variegated shrub morphologies likely reflect specific micro environments that are controlled by water flow rates evaporation and microbial activity the latter processes influenced shrub fabric and morphology under high flow conditions co 2 degassing is the main process leading to carbonate precipitation consequently denser and tightly packed morphologies will precipitate composing mainly the crust lithotype in this scenario microbes are less dominant dendriform shrubs with narrow wide and fili morphologies are interpreted to occur in moderate to low energy water flows narrow dendriform shrubs reflect faster flowing conditions with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs slow to very slow flowing waters are more characteristic for the arborescent arbustiform and pustular shrubs that possibly are highly influenced by evaporation a decrease of water flow likely allows higher microbial activity and consequently shrub morphologies become more fragile and enriched in peloidal micritic aggregate fabrics

ammonite correlation of the uppermost campanian of western europe the u s gulf coast atlantic seaboard and western interior and the numerical age of the base of the maastrichtian

late maastrichtian paleoenvironments and dinosaur biogeography in the western interior of north america during late maastrichtian time three major sedimentary depositional provinces existed in continental environments of the western interior region of north america the sediments accumulated within these provinces are herein termed the piedmont alluvial plain and coastal lowland lithosomes these sedimentary lithosomes correspond to broad paleoenvironmental and paleophysiographic provinces that resulted from the westward shift of the pacific coast the bisection and retreat of the interior epeiric sea and the development of an intermontane basin system during maastrichtian time these dramatic physiographic changes created environments markedly different from those that had prevailed during most of the late cretaceous when western north america consisted of a narrow peninsula flanked on the east by a remarkably stable and monotonous coastal plain in conjunction with these physiographic and environmental changes three diverse dinosaur dominated continental vertebrate faunas arose herein termed the leptoceratops triceratops and alamosaurus faunas each was peculiar to a sedimentary environmental province and among them there was little interchange the separation of these faunas indicates that the dinosaur dominated communities had adapted to changing or deteriorating environmental conditions at the close of cretaceous time the alamosaurus fauna characterized markedly seasonal semi arid environments of the intermontane basins south of about 35 n latitude the triceratops fauna inhabited humid coastal floodplains and swamps bordering the retreating northern embayment of the epeiric sea north of latitude 35 n the leptoceratops fauna inhabited cool piedmont environments flanking the mountainous cordilleran overthrust belt north of 35 n latitude recognition of this biogeographic zonation indicates that the triceratops biozone is only of local utility and that the biostratigraphy of upper cretaceous continental deposits in north america must reflect the provincialism now recognized moreover the evident adaptability of dinosaur faunas to varied and changing environmental conditions suggests that climatic change alone may not have been responsible for their demise

dating a variscan pressure temperature loop with staurolite staurolite with a complex internal metamorphic and structural relationship occurs in metapelite from the silvretta thrust sheet eastern alps stepwise leaching of a core and rim fraction of a single staurolite crystal resulted in a total pb pb isochron of 308 28 ma the variscan metamorphism has been confirmed by a further single bulk staurolite pb pb age of 298 42 ma which is in accordance with u pb ages of 306 8 ma and 304 6 ma respectively obtained from combined u pb leaching of the same crystals direct dating of the staurolite in reaction isograd was therefore successful our results date the prograde part of a variscan counterclockwise pressure temperature path in the silvretta thrust sheet proximity with white mica rb sr and k ar cooling ages suggests that the whole variscan episode was fast and took place within a few million years

magnetostratigraphic and biostratigraphic correlation of late campanian and maastrichtian marine and continental strata from the red deer valley to the cypress hills alberta canada two stratigraphic sequences red deer valley and cypress hills sections in alberta spanning the late campanian to paleocene are magnetostratigraphically and biostratigraphically characterized the red deer valley section had previously been studied but additional material has allowed the extension of the magnetozonation downwards into the bearpaw formation higher sample resolution has allowed the identification of a number of magnetosubzones in 32n 32r and 33n four reversed magnetosubzones have been identified in magnetozone 32n in addition to the one presently recognized in geomagnetic polarity time scales one normal subzone in 32r and one reversed subzone in 33n have also been recorded the 32r 33n boundary is shown to occur in the baculites cuneatus zone the campanian maastrichtian boundary is indicated to be at or near the baculites eliasi baculites baculus boundary at the top of 32n comparisons of the biostratigraphy between the two areas indicate that palynomorph ranges differ from data p

shrub and pore type classification petrography of travertine shrubs from the ballik belevi area denizli sw turkey petrographical and petrophysical properties of the turkish ballik belevi travertine shrubs demonstrate the necessity of reservoir oriented classifications for shrub related lithotypes and associated pore types the presented shrub related lithotype classification incorporates morphology size and fabric which are linked to specific pore types and sizes the travertines show highly complex pore networks as observed from computed tomography reconstructions making them of interest for the development and optimization of pore characterization methodologies and techniques following an upscaling approach porosity 3 15 and permeability 0 505 md strongly vary for the ballik belevi travertines the highest porosities and permeabilities are measured for horizontal samples dominated by slightly dissolution enlarged intershrub and interdigit growth framework porosity mostly found for dendritic shrubs the presented shrub and pore type classification can be applied to shrubs worldwide studying outcrop analogues of continental carbonates helps to better understand heterogeneities lateral variability and properties of pre salt cretaceous continental carbonate reservoirs offshore brazil and angola

mono sample pb pb dating of pyrrhotite and tourmaline proterozoic vs archean intracratonic gold mineralization in zimbabwe gold sulfide tourmaline associations are characteristic of large gold resources worldwide such parageneses can rarely be dated hence genetic models are based on weak age constraints stepwise pb leaching enabled direct precise dating of individual samples of hydrothermal pyrrhotite 1 93 0 05 ga and paragenetically older tourmaline 2 02 0 02 ga from a shear zone hosted gold mineralization within the archean zimbabwe craton these ages reveal a multistage proterozoic hydrothermal event within the craton the presence of a scheelite tourmaline ore dated at 2 65 0 01 ga within the same shear zone may point to an archean precursor because of its capability to demonstrate pb isotope dis equilibrium between associated phases single mineral pb leaching also traces genetic processes

re os sm nd u pb and stepwise lead leaching isotope systematics in shear zone hosted gold mineralization genetic tracing and age constraints of crustal hydrothermal activity abstract a combined re os sm nd u pb and stepwise pb leaching pbsl isotope study of hydrothermal mo w bearing minerals and base metal sulfides from two adjacent shear zone hosted gold deposits ran kimberley in the harare shamva greenstone belt zimbabwe constrain the timing of the mineralizing events to two periods during an initial late archean event 2 60 ga a first molybdenite scheelite bearing paragenesis was deposited in both shear zone systems followed by a local reactivation of the shear systems during an early proterozoic 1 96 ga tectono thermal overprint during which base metal sulfides and most of the gold was re deposited while pbsl has revealed an open system behavior of the u pb systematics in molybdenite and wolframite from the ran mine initial archean re os ages are still preserved implying that this system in these minerals was more resistant to the overprint a similar retentivity could be shown for the sm nd system in scheelite and powellite associated with the above ore minerals re os isotopic data from the proterozoic mineralization in the kimberley mine point to a recent gain of re most pronouncedly affecting fe rich sulfides such as pyrrhotite a significant re loss in powellitic scheelite an alteration phase of molybdenite bearing scheelite coupled with a marked loss of u in w mo ore minerals complements the observation of a major re uptake in fe sulfides during oxidizing conditions in a weathering environment pyrrhotite under these conditions behaves as an efficient re sink lead isotope signatures from pbsl residues of molybdenite powellite and quartz indicate a continental crustal source and or contamination for the mineralizing fluid by interaction of the fluids with older sedimentary material as represented by the direct host country rocks our investigation reveals the potential of the re os isotopic system applied to crustal hydrothermal ore minerals for genetic tracing and dating purposes the simplified chemical separation of re and os from geological material used in this study together with improvements of chemical yields will enable high precision data to be collected rapidly on crustal material with low os concentrations in the future

a new calibration point for the late cretaceous time scale the 40 ar 39 ar isotopic age of the c33r c33n geomagnetic reversal from the judith river formation upper creataceous elk basin wyoming usa we present a new calibration point for the latest cretaceous time scale an interval that at present contains no well dated polarity reversals the magnetostratigraphy of campanian aged sediments in the northern bighorn basin of wyoming documents a geomagnetic reversal in the upper part of the judith river formation that occurs in direct association with ash fall layers dated by the 40 ar 39 ar method extrapolation based on three new 40 ar 39 ar laser fusion dates from sanidines extracted from the ash fall layers dates the reversal at 79 34 ma thus the geomagnetic reversal in the judith river formation can be confidently correlated to the c33r c33n boundary of the geomagnetic reversal time scale this age estimate is in good agreement with recent time scales that date this polarity interval by interpolation between few and widely spaced calibration points the judith river formation is nonmarine and cannot be correlated regionally by traditional ammonite biostratigraphic methods this st

morphogenesis and microstructure of concrete derived calthemites distributions of calcareous calthemite deposits have been widely documented but depositional processes and the architecture of their internal fabrics are not well understood these concrete degradation products from a case study area in western canada have external morphologies comparable to calcite speleothems formed in natural limestone caves but the internal microstructural architecture and mineralogy are markedly different the mineralogy consists of mostly calcite with secondary halite and minor percentages of trona and portlandite a novel morphogenetic model explains depositional processes resulting in calcareous crusts that follow fractures of an overlying concrete surface and how sufficient structural integrity provided by the internal architecture supports attachment areas of tubular soda straws interiors of these multi cm crusts consist of curvilinear calcite laminae arrayed as sub parallel walls compartmentalizing water gas interfaces along variously interconnected conduits and basin form chambers overall porosities of 40 60 or more are prevalent in contrast to 1 associated with externally similar drapery form crusts deposited within natural limestone caves several calcite fabrics new to calthemite deposits are described including dendritic shrubs that coalesce into concentric growth rings along central canals of soda straws

cave aerosols distribution and contribution to speleothem geochemistry there is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothem this paper provides the first attempt to synthesize the issues processes of cave aerosol introduction transport deposition distribution and incorporation are explored and reviewed from existing literature key issues of specific aerosol processes of distribution and production as well as cave location and morphology effects are highlighted through the presentation of preliminary monitoring data this study identifies the strong relationship between cave ventilation cave aerosols and their consequent spatial distribution the contribution of cave aerosol deposition to speleothem geochemistry is modelled and evaluated using a mass balance framework as an example speleothem trace element data from obir cave austria are compared with aerosol inputs to evaluate their significance the mass balance study demonstrates that generally under normal continuous growth and environmental conditions aerosol deposition will be of only minor importance however it highlights specific scenarios in which aerosol contributions will be significant speleothem hiatuses or slow growth high aerosol deposition and secondary microbiological feedback

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

the influence of high u th inclusions on the u th pb systematics of almandine pyrope garnet results of a combined bulk dissolution stepwise leaching and sem study abstract the isotope systematics of garnet are increasingly being used to define prograde thermal histories in metamorphic belts this approach to geochronology has the distinct advantage that time information is directly related to the pressure temperature deformation history recorded by the same mineral one potential problem with the technique however is that the inventories of radiogenic isotopes apparently measured in garnet separates may be located in inclusions rather than the garnet lattice itself inclusions of old refractory minerals such as zircon may bias the ages to the extent that they are rendered meaningless in terms of dating garnet growth establishing pt histories and constraining tectonic mechanisms in this contribution we present u th pb data obtained on bulk dissolutions of garnet from the himalaya as well as the results of a detailed sem and u th pb stepwise leaching study in order to further clarify these issues our experiment has the advantage that the age difference between the garnets and potential inclusions is very large so that the influence of the latter is highlighted the u th pb data from the bulk dissolutions are highly complex and yield apparent ages ranging from 1000 ma to 30 ma the stepwise leaching study demonstrates that this complexity results from small inclusions of allanite and zircon detected with the sem the bulk of the radiogenic 206pb in these samples was released only by treatment at high pressure in a bomb in addition the 208pb 206pb ratio of the radiogenic pb released in earlier leach steps is inconsistent with the available constraints on the th u ratio of garnet lattices as measured by sims in this case the u pb ages of these garnets is dependent purely on the age of the included high u th phases and the degree to which they have isotopically re equilibrated with the whole rock during the subsequent metamorphism that grew garnet simple mass balance arguments show that in this particular instance very small amounts of these inclusions are required amounts that escape detection during conventional sample preparation these data also have implications for current thinking on the closure temperature for the sm nd and u pb systems in garnet

bacterial shrubs crystal shrubs and ray crystal shrubs bacterial vs abiotic precipitation hot water travertine deposits commonly contain shrub like morphologies on the centimeter to meter scale that range from highly irregular forms bacterial shrubs to features that display regular geometric patterns crystal shrubs and ray crystal crusts the bacterial shrubs have been previously recognized as the product of bacterially induced precipitation whereas the ray crystal crusts have been described as due to dominantly abiotic precipitation the bacterial shrubs have a highly irregular morphology similar to woody plants in contrast end member crystal shrubs display distinct crystal habits and regular repeating morphologies i e they commonly have attributes of noncrystallographic as well as crystallographic dendrites there is a complete gradational relationship between the bacterial shrubs and crystal shrubs ray crystal crusts are large fan shaped features composed of subparallel extremely coarse bladed crystals of calcite all three types bacterial shrubs crystal shrubs and ray crystal crusts contain either a dense tangle of bacterial body fossils and or micron sized pores the micropores are bacterial molds the immediately enveloping spar crystals around all three morphologic types are devoid of bacterial body fossils and micropores the bacterial shrubs crystal shrubs and ray crystal crusts are to differing degrees the product of bacterially induced precipitation as well as abiotic mineral precipitation the differences in morphology are due to the relative contribution of bacterially induced precipitation as compared with that of abiotic mineral precipitation bacterially induced precipitates can form in environments too chemically harsh or otherwise inhospitable for other taxa to thrive epiphyton and renalcis commonly formed in occult environments under conditions inhospitable to other taxa consideration of the published descriptions and interpretations concerning epiphyton and renalcis and by analogy the origin of bacterial shrubs have led to the conclusion that epiphyton and renalcis also are bacterially induced precipitates

polyphase deformation in the western mount isa inlier australia episodic or continuous deformation abstract the polyphase deformation history of the mount novit ranges western mount isa inlier australia involved the development of four generations of n s to nw plunging folds development of which alternated with movement on n s striking faults shear zones with west over east displacement the spatial relationships between successive structures and the distinct similarities in the kinematics style and asymmetry are all consistent with continuous deformation during e w to ne sw shortening additional support for this hypothesis is based on the development of the three major fold generations and the intervening faults and shear zones during low p high t metamorphism although the duration of this metamorphic event cannot be constrained recent studies have linked low p metamorphism to heat advection by migrating melts thermal modelling indicates that such metamorphic events will be short lived in comparison to those associated with thermal relaxation of over thickened crust low p metamorphism is unlikely to persist through two or more separate tectonic events therefore syn metamorphic polyphase deformation in the mount novit ranges apparently formed during a single continuous tectonic episode this structural history differs from both the regional scheme and that of previous workers in this area the main differences are i no evidence was found for early thrust faulting prior to n s folding ii there are four generations of n s to nw se folds as opposed to two and iii this study favors a single consistent tectonic regime in contrast to the interpretation of three discrete isolated tectonic events

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

thrusting and duplex formation at mount isa queensland australia large scale repetition of mount isa and haslingden group rocks in the anticline north of mount isa is interpreted as the core of a thrust duplex which has been subsequently folded parallel to the direction of thrusting displacement of mount isa group rocks above the duplex is extremely significant to the regional geology and exploration for more mount isa style pb zn and cu orebodies interpretation of the geometry of the thrust belt indicates thrusting on different stratigraphical levels below and above the duplex during its formation horses formed from a heelwards protruding footwall ridge instead of a trough and the complex effects on stratigraphical cross sections through duplexes of sloping lateral footwall ramps on horses

late cretaceous to early tertiary magnetostratigraphy of a continental sequence red deer valley alberta canada the red deer valley exposes a conformable 350 m thick late campanian to early paleocene fluvial deltaic coal bearing sequence named the edmonton group systematic sampling and paleomagnetic analysis of the dominant lithologies mudstones sandstones and shales were carried out over five sections correlated by coal seams to provide some 500 sites stratigraphic levels primary detrital remanent magnetization directions after alternating field cleaning produce a polarity reversal pattern correlatable to sea floor magnetic anomalies 29 33 the campanian maastrichtian boundary based upon the first appearance of wodehouseia and the maastrichtian paleocene cretaceous tertiary boundary based upon an ir anomaly associated with dinosaur and cretaceous palynofloral extinctions correlate closely magnetostratigraphically with the marine foraminiferal section at gubbio italy radiometric dating of bentonites has indicated the ages of these boundaries to be approximately 71 and 64 ma respectively