apatite feldspar u pb thermochronometer a reliable mid range 450 c diffusion controlled system the u pb systematics of apatite are commonly dominated by simple volume diffusion without secondary growth and recrystallization that can affect u pb systematics of sphene monazite and zircon although apatite is a relatively low u mineral both u and pb are lattice bound and thus the u pb systematics are not controlled by micro inclusions as appears to be the case for other low u minerals such as garnet and staurolite closure temperature estimates from both experimental and empirical studies range from 425 c to as high as 500 c for typical diffusion radii 25 m and cooling rates 2 100 c ma respectively this range can be exploited to constrain cooling and exhumation histories of both igneous and metamorphic rocks in addition the closure temperature for pb diffusion in apatite fills a gap between that for pb diffusion in sphene 650 c and diffusion of ar in hornblende 500 c muscovite 350 c and biotite 300 325 c apatite is a common accessory phase in many rock types and u pb apatite dating can be a reliable and powerful thermochronometer as it combines mid range cooling ages with the strength of the u pb system in testing for isotopic closure precisions of u pb apatite dates can range from 1 2 to as low as 0 3 for proterozoic or archean dates the main limitation to accuracy of u pb apatite dates is a moderate to low ratio of u to pb and corresponding dependence of concordia coordinates on the choice of initial pb isotopic composition for proterozoic aged samples with measured 206pb 204pb of 100 the range of geologically reasonable initial pb isotopic compositions can shift the calculated u pb age by 60 ma fortunately even though the diffusion rate of pb in alkali feldspar is less than in apatite it appears that the isotopic composition of pb in coexisting feldspar is a good approximation of the initial isotopic composition in apatite for many geologic settings examples are given from an archean terrane in se wyoming that was unroofed and cooled during proterozoic uplift and from proterozoic terranes in sw us that have contrasting thermal histories

late diagenetic redistribution of uranium and disturbance of the u pb whole rock isotope system in a black shale the middle ordovician llandeilo caradoc formation black shales deposited at about 460 ma on the southwest margin of the welsh basin show evidence of a late diagenetic uranium redistribution event evidence for this redistribution event includes a disturbance in the u pb whole rock isotopic system at about 193 ma marked by a large range in the whole rock 238 u 204 pb between 2 and 90 one explanation for this large range is that individual whole rocks have experienced either a gain or a loss of u at the time of the disturbance this hypothesis is supported by the large range in measured u contents from the llandeilo caradoc formation black shales 0 16 to 6 6 ppm upper crust 2 8 ppm post archean average shale paas 3 1 ppm taylor and mclennan 1985 uranium that was likely sequestered during deposition and early diagenesis has been redistributed on a greater than whole rock scale centimeters to meters the u pb isotope systematics identified in this study and other pb isotope data from the welsh basin evans 1996 constrain a reasonable u concentration of 2 91 ppm for an unaltered llandeilo caradoc shale at the time of deposition 460 ma assuming 2 91 ppm to be an average u content at the time of deposition some rocks in the llandeilo caradoc formation have lost as much as 95 of the u likely present at the time of deposition and early diagenesis whereas others exhibit an almost equal enrichment when the u pb isotopic and elemental data from whole rocks and individual u bearing phases i e carbonate apatite monazite organic matter are examined in conjunction with the paragenetic sequence controls on the distribution of u in the llandeilo caradoc whole rocks and a pattern of open system conditions become apparent despite the presence of potential u rich diagenetic phases such as apatite and monazite most of the u in the relatively enriched samples is associated with a non extractable unidentified diagenetic component uranium mass balance considerations and whole rock u pb isotope systematics require that the non extractable component formed at about 193 ma during a late diagenetic uranium redistribution event the redistribution of u within the llandeilo caradoc formation has important implications for the use of u rich sedimentary minerals as geochronometers and for the use of u as a paleo redox indicator specifically a trace element indicator like uranium may in some cases record information about the postdepositional history of a sedimentary rock rather than document the absolute timing and conditions of deposition moreover this unique history can be properly evaluated only through an integrated petrographic geochemical approach that can discern the distribution and source i e depositional versus diagenetic of u in an individual whole rock

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

cerium anomaly and th u fractionation in the 1 85 ga flin flon paleosol clues from ree and u rich accessory minerals and implications for paleoatmospheric reconstruction the 1 85 ga paleosol at flin flon manitoba canada was one of the first paleoweathering profiles taken as evidence for a dramatic rise in the oxygen content of the paleoproterozoic atmosphere diagenesis and greenschist facies metamorphism have modified the abundances of some major elements e g k and fe in the flin flon paleosol inductively coupled plasma mass spectrometry icp ms analyses reveal a positive ce anomaly on both chondrite and amisk basalt normalized ree patterns and marked th u fractionation in the uppermost maroon paleosol the ce anomaly is confirmed by the occurrence of cerianite and by the compositions of other ree and u rich accessory minerals i e secondary monazite and uraninite in the uppermost maroon paleosol th u fractionation is supported by the presence of uraninite in both the paleosol and overlying missi sedimentary rocks chemical ages of uraninite 1 85 to 1 0 ga suggest that this mineral might have formed during weathering or diagenesis but was susceptible to disturbance although igneous monazite and zircon are well preserved in even the uppermost maroon paleosol primary fluorapatite exhibits variable degrees of weathering in the basal green paleosol and has been obliterated completely in the upper maroon paleosol published paleomagnetic data suggest a tropical paleolatitude for the flin flon region at the time of formation of the paleosol the positive ce anomaly in the flin flon paleosol confirms previous studies for an oxic atmosphere p o 2 10 1 5 to 10 2 pal at 1 85 ga however extreme caution must be exercised in the interpretation of th u fractionation in paleosols moreover this study demonstrates the advantage of a detailed characterization of ree and u rich accessory minerals in the application of trace element geochemistry of paleosols for paleoatmospheric reconstruction eh ph diagrams for the stabilities of cerianite and uraninite in their respective systems ce p c h o and up c h o at 25 c and 1 bar reveal the importance of phosphate complexes in the formation of ce anomalies and th u fractionation in both modern and ancient weathering environments

postdepositional sm nd fractionation in sandstones implications for neodymium isotope stratigraphy abstract sandstone reservoirs from the norwegian continental shelf commonly show varying degrees of postdepositional fractionation of sm nd ratio apparently due to preferential incorporation of sm in the crystal lattice of diagenetic apatite based on data from leaching experiments an apatite mineral separate and petrography it is proposed that fractionation occurred mainly during closed system burial diagenesis as phosphate deposited on the sea floor recrystallized to apatite and incorporated rare earth elements ree from the surrounding rock matrix as a result the sm nd model age parameter in general contains two components of information a the true crustal age of the sediment and b a secondary component of sm nd fractionation which can be either negligible or dominant it is difficult to separate these components and thus correct for component b even in data showing no obvious signs of postdepositional fractionation model ages may be variably disturbed by subordinate amounts of diagenetic alteration however the isotope ratio 143nd 144nd is expected to be relatively resistant to alteration by secondary sm nd fractionation and should therefore be used rather than model age as the principal correlation parameter in stratigraphic studies in this way nd isotope stratigraphy can still be used as a valuable and unique tool for studies of provenance and correlation even in strata showing strong sm nd fractionation effects strongly sm nd fractionated horizons recognized by bulk rock sm nd ratios 0 23 may also be useful for stratigraphic correlation but it is clear that their occurrence reflects special depositional conditions rather than shifts in sediment provenance

climatic and oceanic changes during the middle late ordovician transition in the tarim basin nw china and implications for the great ordovician biodiversification event abstract the middle late ordovician transition darriwilian to sandbian age witnessed a major pulse of the great ordovician biodiversification event gobe and distinctive oceanic geochemical fluctuations such as coeval negative c and sr isotope excursions in this study investigations into geochemical variations notably the hg abundance or hg toc have been carried upon the organic rich black shale of the middle upper ordovician saergan formation to unravel the causes of this pulse based on these data three phases were identified phase 1 0 to 3 m is characterized by rising hg toc up to 138 ppb wt and ti al values as well as high ciacorr corrected chemical index of alteration values 68 9 72 3 with negligible enrichment of redox sensitive elements rse and nutrient elements e g u 5 2 ppm v 153 ppm mo 1 8 ppm p2o5 0 2 suggesting intensified volcanism which could have emitted significant amounts of greenhouse gases thereby leading to climate warming in contrast phase 2 3 to 11 m is characterized by decreasing hg toc and ti al ratios relatively low though slightly fluctuating ciacorr values generally depleted in rse except moderately enriched u up to 14 6 ppm and increased p al and ba al ratios implying weakening volcanic activity and subsequent climate cooling and the potential for improved seawater ventilation as a result of oceanic upwelling phase 3 sandbian age 11 13 m witnessed continuous decrease in hg toc ratio an increase in ti al and ciacorr values fairly low values of rse enrichment and p al and ba al ratios indicating recurrent climate warming and the potential for slowed oceanic circulation and attenuated upwelling of nutrient rich deep waters onto the shallow shelf these changes could have diminished bioproductivity and organic output onto the seafloor this study offers insights into volcanic climatic oceanic interactions during a major pulse of the gobe around the middle late ordovician transition while black shales were extensively deposited

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

a comparison of climatological subseasonal variations in the wintertime storm track activity between the north pacific and atlantic local energetics and moisture effect distinct differences of the storm track jet relationship over the north pacific and north atlantic are investigated in terms of barotropic and baroclinic energetics using ncep 2 reanalysis data for the period of 1979 2008 from fall to midwinter the pacific storm track pst activity weakens following the southward shift of the pacific jet whereas the atlantic storm track ast activity remains steady in position and intensifies regardless of the slight southward shift of the atlantic jet this study is devoted to seeking for the factors that can contribute to this conspicuous difference between the two storm tracks on climatological subseasonal variation by analyzing eddy properties and local energetics different eddy properties over the two oceans lead to different contribution of barotropic energy conversion to the initiation of storm tracks in the north atlantic meridionally elongated eddies gain kinetic energy efficiently from stretching deformation of the mean flow in the jet entrance on the other hand the term associated with shearing deformation is important for the initiation of pst analysis of baroclinic energetics reveals that the intensification of the ast activity in midwinter is mainly attributed to coincidence between location of maximum poleward and upward eddy heat fluxes and that of the largest meridional temperature gradient over slight upstream of the ast the relatively large amount of precipitable water and meridional eddy moisture flux along baroclinic energy conversion axis likely provides a more favorable environment for baroclinic eddy growth over the north atlantic than over the north pacific in the meantime the midwinter minimum of the pst activity is attributable to the southward shift of the pacific jet stream that leads to discrepancy between core region of poleward and upward heat fluxes and that of meridional thermal gradient weakening of eddy mean flow interaction due to eddy shape and reduction of moist effect are also responsible for the weakening of storm track activities in midwinter when the strongest baroclinicity exists over the north pacific

representation of northern hemisphere winter storm tracks in climate models northern hemisphere winter storm tracks are a key element of the winter weather and climate at mid latitudes before projections of climate change are made for these regions it is necessary to be sure that climate models are able to reproduce the main features of observed storm tracks the simulated storm tracks are assessed for a variety of hadley centre models and are shown to be well modelled on the whole the atmosphere only model with the semi lagrangian dynamical core produces generally more realistic storm tracks than the model with the eulerian dynamical core provided the horizontal resolution is high enough the two models respond in different ways to changes in horizontal resolution the model with the semi lagrangian dynamical core has much reduced frequency and strength of cyclonic features at lower resolution due to reduced transient eddy kinetic energy the model with eulerian dynamical core displays much smaller changes in frequency and strength of features with changes in horizontal resolution but the location of the storm tracks as well as secondary development are sensitive to resolution coupling the atmosphere only model with semi lagrangian dynamical core to an ocean model seems to affect the storm tracks largely via errors in the tropical representation for instance a cold sst bias in the pacific and a lack of enso variability lead to large changes in the pacific storm track extratropical sst biases appear to have a more localised effect on the storm tracks

a petrographic approach for evaluating trace element mobility in a black shale abstract at the time of deposition black shales record geochemical information related to the provenance and conditions of deposition for that rock these initial geochemical conditions are susceptible to alteration and overprinting by the aggressive processes of black shale diagenesis in this study we evaluate a sequence of ordovician black shales from the southern welsh basin for the presence of such a diagenetic overprint through use of cathodoluminescence backscattered electron imaging reflected light microscopy fission tracks and microprobe elemental mapping we can discern textural relationships with in the welsh black shales the relationships observed constrain a paragenetic sequence and overall diagenetic history including the early diagenetic formation of pyrite apatite rare earth element ree rich and carbonate and later formation of diagenetic monazite ree u rich and late stage carbonate the chemical reactions necessary to produce this mineral sequence require postdepositional redistribution of ree including changing cerium anomalies ce ce and uranium as a result ree u and their associated isotopic systems sm nd and u pb can reflect a diagenetic overprint rather than the source area and depositional conditions the paragenetic sequence described in this study records several postdepositional changes in the whole rock mineralogy among these changes are the formation of ree rich apatite and ree and u rich monazite the formation of these phases requires that ree and u are being redistributed on at least a mineral scale and that the initial depositional and provenance information recorded by the whole rock has been disturbed therefore the approach used in this study to carefully characterize the paragenetic sequence from the llandeilo caradoc black shales should be considered necessary in order to fully evaluate the usefulness of trace element proxies susceptible to diagenetic redistribution

orogenesis vs diagenesis can we use organic rich shales to interpret the tectonic evolution of a depositional basin abstract black shales from the southern appalachian basin and the southwest welsh basin have anomalous u pb and nd model ages suggesting syn and post depositional resetting of the sm nd and u pb isotopic systems this alteration to the primary detrital signature of these two shale sequences is indicative of black shale diagenetic depositional processes that obscure paleo environmental and provenance information recorded prior to and during deposition the trace element and isotopic signatures of these two shale sequences reveal a syn post depositional history that is de coupled from the coeval orogenic history of the region making it difficult to reconstruct the tectonic and oceanographic conditions present at the time of deposition both the ordovivian welsh basin and the devonian appalachian basin sequences host ree and u bearing diagenetic phosphate minerals that play a critical role in the whole rock ree and u budgets in the welsh basin shales early diagenetic apatite and a later monazite phase dominate the ree budget and cause the redistribution of ree early in the basin s history ca 460 ma this redistribution is recorded by the sm nd system 450 90 ma and the nd model ages that are anomalously old by as much as 20 t dm 2 0 ga this early history is complicated by a permo triassic fluid event affecting the whole rock u budget and resetting the u pb isotopic system at 193 45 ma the appalachian basin sequence appears to have a much less complicated history yet still records a significant disturbance in both the sm nd isotopic system 392 76 ma and the pb isotopic system 340 50 ma at about the time of deposition ca 365 ma these two sequences suggest a pattern of diagenetic disturbance common to black shales these processes are unique to black shales and must be considered when interpreting provenance and paleo environmental information from the black shale sequences although these rocks are susceptible to alteration the alteration may provide extensive information on the post depositional history of the basin while still retaining some primary depositional information if black shale processes are considered during the interpretation of isotopic and trace element signatures from organic rich shales it may be possible to recover an extensive basin history

weathering of fruchtschiefer building stones mineral dissolution or rock disaggregation building stones manufactured from contact metamorphic slates fruchtschiefer slate from theuma sachsen germany were investigated for mineralogical alterations as well as for changes in porosity and surface roughness due to weathering after weathering periods of several years to decades the originally dark gray colored slates show pale spots of several centimeters in size at the surface of building stones the dark colored and light colored sections of the slate show no differences in mineralogy surface weathering did not result in newly precipitated minerals it was also found that the observed differences in color are not caused by variations in sedimentary organic carbon concentration or in sulfide sulfate concentrations obtained results instead indicate that dark surface sections may show a thin cover of recent organic matter om e g living om soot dirt etc microscopic investigations suggested that this cover was exfoliated at light colored surface sections the observed disaggregation of the upper 2 mm of the building block material results in an increase in porosity porosity of black unweathered slate is 1 m show a significant increase in frequency compared to the original pore size distribution porosity of weathered rock volumes increased to approx 8 vol discolored surface sections show a higher surface roughness root mean square roughness rq 1 m compared to dark colored slate surfaces rq 200 nm both data are for cleavage planes preferentially the discolored surface sections are located close to the edges of cut stones this and the alteration in porosity pore size and surface roughness indicate that color changes of the slate are largely influenced by rock disaggregation proceeding from the edges into the center rather than by mineral dissolution precipitation processes

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

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

long lived lree mobility in the cratonic rift and foredeep to foreland sedimentary cover at the western margin of the karelia province abstract the western margin of the karelia province of the fennoscandian shield consists of archean crust covered by remnants of paleoproterozoic c 2 5 1 9 ga metasedimentary rocks the study area in the eastern part of the margin shows 2 3 2 1 ga cratonic sedimentation followed by 2 1 2 05 ga rift sedimentation and c 1 91 1 92 ga foredeep to foreland sedimentation related to continent arc continent collision extreme lree mobility loss up 95 of la is recorded by many samples from these units monazite bastnasite and in some cases allanite have been the prealteration lree host phases in the lree depleted samples monazite was altered to th silicates with variable loss of the lree the remaining part of which was incorporated in th poor monazite the depositional age of the sedimentary units was studied by dating la mc icpms detrital zircon grains and the age of lree mobility by dating monazite and xenotime and by whole rock sm nd modeling the maximum deposition age of the foredeep to foreland basin is 1 91 1 92 ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1 87 1 86 ga based on the younger age limit of late to post tectonic xenotime and the ages of few probable metamorphic zircons coeval bastnasite with xenotime in a lree enriched sample suggests that this was also one important stage of lree mobility monazite crystallizations have occurred 1 76 1 78 ga ago while the rb sr whole rock data suggest that the closure of this isotope system took place 1732 21 ma ago the sm nd modeling gives ages at 0 4 1 0 ga for lree depletion the sm nd age of 412 27 ma can be considered as the age of the latest major lree depletion event we propose that alkali bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2 3 2 1 ga alkalinity of fluids was later increased by interaction with alkaline 2 05 ga source materials before and during the c 1 91 1 92 ga foredeep to foreland basin stage basin inversion and metamorphic crystallization occurred at 1 91 1 87 ga episodes of fluid migration at 1 78 1 73 ga and afterwards were focused along fracture zones and in microfracture networks the 0 4 ga stage is the most prominent of the

assessing the impact of black shale processes on ree and the u pb isotope system in the southern appalachian basin abstract upper devonian java and huron shales from the southern appalachian basin exhibit evidence of ree redistribution and resetting of the u pb isotopic system at the time of deposition ca 365 ma this alteration to the primary detrital signature of these shales is indicative of black shale diagenetic depositional processes that in effect obscure paleoenvironmental and provenance information that may be recorded the most direct evidence of these black shale processes is the rotated nature of the whole rock ree patterns from this sequence of presumably source related shales the neo formation of ree bearing diagenetic phases such as apatite and possibly carbonate has led to an unusually large range in the whole rock 147 sm 144 nd and the ce ce for this sequence of shales changes to these whole rock ratios will effectively alter the nd model age and create a ce ce that records evidence of diagenetic processes rather than information about the paleooceanographic conditions of the basin simultaneously the sequestration of u at the time of deposition and subsequent fixation in diagenetic phases such as apatite has effectively reset the 238 u 206 pb isotopic system at 340 50 ma overprinting the pb isotopic signature of the source area the trace element and isotopic signatures recorded by the java and huron formation shales from the study area reveal a syn postdepositional history dominated by what can be referred to as black shale processes the diagenetic conditions that develop at and below the sediment water interface during the deposition of organic rich shale are unique and consequently leave behind a unique geochemical fingerprint that can potentially overprint paleoenvironmental and provenance information

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

nd and pb isotopic evidence for provenance and post depositional alteration of the paleoproterozoic huronian supergroup canada neodymium model ages for fine grained formations of the paleoproterozoic huronian supergroup mckim pecors gowganda gordon lake range from 3 00 to 2 55 ga and indicate a provenance dominated by the late archean superior province to the north and west the stratigraphically highest unit gordon lake formation has a distinctive nd isotopic composition with tdm being 100 400 ma younger than underlying mudstones this suggests that the provenance changed consistent with a previously documented change towards more negative eu anomalies in the gordon lake lead isotopes are consistent with a superior province provenance and in addition provide evidence for two episodes of regional post depositional disturbance of the u pb system lower huronian mckim pecors samples align along 207pb 204pb 206pb 204pb slopes equivalent to 2170 58 ma mswd 92 n 9 and 2212 92 ma mswd 9 1 n 5 respectively these ages are at the minimum age limit on sedimentation and within uncertainty of the nipissing diabase 2219 4 ma a ubiquitous regional feature parts of which may have intruded while much of the huronian was unconsolidated these pb pb ages are interpreted to represent widespread diagenetic processes possibly associated with an early phase of nipissing intrusion 206pb 204pb varies mostly from 19 to 34 up to 59 whereas implied 232th 238u are mostly between 2 and 4 only slightly below the upper crustal value of 4 changes in 206pb 204pb imply changes of 238u 204pb by factors of 2 and up to 12 5 values for are also in the range 2 4 and accordingly pb loss appears to dominate this disturbance elevated 206pb 204pb correlates with post depositional addition of potassium in the gordon lake and possibly the gowganda formations k metasomatism has been demonstrated previously in the underlying serpent formation and in paleosols developed at the unconformity beneath the huronian supergroup the latter being dated at 1690 1730 ma widespread metasomatism resulting in k addition and pb loss may have been related to northerly directed basin wide fluid movement in response to post tectonic intrusions and erosion of the ca 1 85 ga penokean orogen to the south since pb isotope systematics in the lower huronian mudstones appear unaffected apart from natural conduits provided by unconformity surfaces and possibly lower huronian sandstone aquifers that also may have been affected by k metasomatism it appears that fluid movement was more pervasive in the upper levels of this sedimentary sequence

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

park forest l5 and the asteroidal source of shocked l chondrites the park forest l5 meteorite fell in a suburb of chicago illinois usa on march 26 2003 it is one of the currently 25 meteorites for which photographic documentation of the fireball enabled the reconstruction of the meteoroid orbit the combination of orbits with pre atmospheric sizes cosmic ray exposure cre and radiogenic gas retention ages cosmic histories is significant because they can be used to constrain the meteoroid s birth region and test models of meteoroid delivery using he ne ar 10be and 26al as well as a dynamical model we show that the park forest meteoroid had a pre atmospheric size close to 180 g cm 2 0 40 porosity and a pre atmospheric mass range of 2 6 tons it has a cre age of 14 2 ma and u th he and k ar ages of 430 90 and 490 70 ma respectively of the meteorites with photographic orbits park forest is the second after novato that was shocked during the l chondrite parent body lcpb break up event approximately 470 ma ago the suggested association of this event with the formation of the gefion family of asteroids has recently been challenged and we suggest the ino family as a potential alternative source for the shocked l chondrites the location of the lcpb break up event close to the 5 2 resonance also allows us to put some constraints on the possible orbital migration paths of the park forest meteoroid

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

in situ u pb dating and element mapping of three generations of monazite unravelling cryptic tectonothermal events in low grade terranes abstract in situ u pb dating of monazite and xenotime in sedimentary rocks from the mid archean soanesville group in the pilbara craton yields ages for provenance diagenesis and multiple low grade metamorphic events detrital monazite and xenotime grains give dates 3250 ma whereas diagenetic xenotime provides a new minimum age of 3190 10 ma for deposition of the basal soanesville group previously constrained between 3235 ma and 2955 ma metamorphic monazite provides evidence for three episodes of growth at 2 88 2 16 and 1 65 ga element mapping of monazite for la sm y and th reveals distinct cores and rims in some crystals that were used to guide the placement of analytical spots during in situ u pb dating by sensitive high resolution ion microprobe shrimp specifically la and sm distributions closely correlate with different generations of monazite the presence of two generations in single monazite crystals highlights the need for characterizing mineral chemistry prior to geochronology it also shows the importance of using in situ dating techniques rather than methods that rely on the analysis of entire potentially multi aged crystals the ages recorded by metamorphic monazite span more than one billion years and are interpreted to record cryptic tectonothermal events within the craton the 2 88 ga age coincides with a phase of regional deformation metamorphism and gold mineralization along a major crustal lineament whereas the most common monazite age population at 2 16 ga corresponds with the migration of a foreland fold and thrust belt across the craton the youngest age 1 65 ga coincides with an episode of tectonic reworking in the capricorn orogen along the southern pilbara margin the prolonged history of monazite growth may in part relate to channelized fluid flow during reactivation of long lived n to ne trending crustal structures that transect the craton despite repeated episodes of metamorphism the isotopic system in each generation of monazite remained unperturbed yielding precise dates the ability of monazite to record three separate events and in some instances two events in a single crystal distinguishes it from most other low temperature mineral chronometers which are readily reset during metamorphic overprinting low temperature monazite geochronology can provide a detailed isotopic history of cryptic thermal events and reveal the temporal and spatial patterns of far field fluid flow related to tectonic processes the previously unrecognized history of crustal fluid flow in the pilbara craton has implications for chemical mineralogical and isotopic studies seeking to understand conditions on the early earth

new constraints for the source characteristics deposition and age of the 2 1 1 9 ga metasedimentary cover at the western margin of the karelian province abstract the paleoproterozoic cover sequence at the 100 150 km wide western margin of the archean karelian province is dominated by deep water lower and upper kaleva metasediments we present here an interpretation of sm nd isotope and geochemical data on 36 samples tims multi grain u pb zircon analyses on nine samples and ca 100 sims analysis of detrital zircon grains from four upper kaleva and one lower kaleva samples the lower kaleva is characterized by autochthonous parautochthonous lithologically heterogeneous metaturbidites showing common enrichment in quartz all the analysed detrital zircons are of a local neoarchean source but tdm variation up to 2 4 ga combined with geochemical data indicate abundant mixing of paleoproterozoic mafic material presumably from 2 1 ga plateau lavas and dykes in most of the lower kaleva samples the upper kaleva is dominantly allochthonous with tectonically enclosed fragments of ophiolite bodies and it is characterized by lithological and geochemical isotopic homogeneity geochemical isotopic and detrital zircon data favour material derived from an orogenic domain comprising both archean and proterozoic units followed by effective mixing during the transport the archean zircon grains 25 are mostly neoarchean the paleoproterozoic grains lack zircons at 2 5 2 2 ga and plot dominantly 92 between 1 92 and 2 05 ga the indicated maximum deposition ages vary from 1 95 1 94 ga to 1 92 ga the main source area proposed is the himalaya type lapland kola orogen now in the northeast which experienced mountain building and erosion at 1 95 1 91 ga the western margin of the karelian province shows evidence of rifting and lithosphere thinning from 2 1 to 1 95 ga but it is still under debate whether the craton breakup occurred at 2 06 ga in a volcanic or later at 1 95 ga in a non volcanic margin setting one hypothesis is that the onset of collision in the northeast changed plate motion and lead to a new spreading within the pre existing passive margin at 1 97 1 95 ga thus both a volcanic margin at 2 06 ga and a non volcanic margin at ca 1 95 ga could have been operated at the western margin of the karelian province

ree and their relevance to the development of the kupferschiefer copper deposit in poland abstract over one hundred samples representing mainly clayey organic and carbonate rich shales kupferschiefer but also other members of different ore sections including hangingwall dolomites z1 werra and footwall weissliegend sandstone lower permian have been collected in different mines of the lubin glogow mining district mainly near the contact transitional zone between the copper mineralized zone and secondarily oxidized rote faule rf zone in general the polish kupferschiefer shales are enriched in mree in comparison to nasc in a typical copper rich ore section the ree amounts and patterns depend on lithologies being generally similar in shales and dolomite ree vary among sandstones shales and dolomites average 73 143 and 85 ppm respectively probably reflecting mainly their clay contents sandstones have strongly convex ree patterns with positive eu and negative gd anomalies and depletion in lree and enrichment in mree relative to hree the ree patterns of shale and dolomite are similar to one another and rather flat with strong negative eu anomalies and a small positive gd anomaly in the case of shales the ree patterns of shales from the mineralized cu zone are generally convex mree enriched and have negative eu anomalies however in a section with cu zn and pb shales the ree pattern of pb bearing shales shows a positive eu anomaly in contrast to other shales and overlying dolomite more oxidizing conditions of deposition can be assumed for pb shales no significant differences between ree distributions in transitional and oxidized zones have been observed their ree patterns are more convex and are much higher av 247 ppm than those in the mineralized zone and they do not show eu anomalies the strongly convex pattern may suggest either enrichment in mree or relative depletion in lree due to localized precipitation of light ree minerals both in shales and in the uppermost part of the sandstones two unique sections one cu rich and one cu lean partly oxidized comprising three shale beds interbedded with dolomites have been compared generally ree contents are similar in these two sections also similar are changes in contents of ree between beds in both sections which decrease significantly upwards from 157 171 ppm to 54 60 ppm the ree patterns of the lowermost beds directly overlying sandstones are ramp like with lree enrichments the upper beds have concave ree patterns comparison between sections shows generally stronger negative eu and positive gd anomalies in the highly mineralized section there is a highly significant positive relationship between cu and ree contents in cu rich shales and slightly less significant negative relationship for their concentration in oxidized and transitional shales there is a moderate significant positive correlation between p 2 o 5 and ree contents in cu rich shales the observed differences in ree contents cannot be provenance dependent but have been caused by diagenetic processes possibly related to mineralization and oxidation processes europium anomalies generally reflecting different eh conditions in the deposit can be eliminated by the prolonged oxidation strong enrichment of the rf zones in ree may result from their desorption from large volumes of oxidizing including mineralizing solutions which probably emerged from the underlying molasse lithologies into the rote faule areas higher contents of ree in the lowermost shales suggest upward movement of solutions from the underlying sandstones also far away from the rf areas

elemental mobility in phosphatic shales during concretion growth and implications for provenance analysis shale normalized rare earth element ree patterns record variable redox conditions in coprolitic phosphorite concretions and their host shales from the pennsylvanian age cyclothems in the u s midwestern states of oklahoma kansas nebraska iowa and ohio as well as the mississippian age fayetteville shale of arkansas shale normalized enrichments in middle ree mree developed as the phosphatic concretions lithified under reducing conditions in pore waters of organic rich muds depletions in mree sm ho in host shales correspond to the mree enrichments in some nearby concretions rare and weak negative cerium depletions in both reworked and unreworked phosphorite concretions suggest exposure to oxygenated waters positive europium anomalies in thick phosphorite coatings on coprolitic phosphorite concretion cores suggest extreme reduction during lithification of the phosphorite coating flat ree patterns in both host shales and phosphorite concretions probably reflect detrital influence phosphate diagenesis can affect the trace element chemistry of black shale enough to alter provenance signals overall enrichment in ree in phosphorite relative to host shale suggests movement of ree as does the mree enriched phosphorite near the mree depleted host shale diagenetically mobile ree can affect la th sc relationships used in provenance analysis the extent of the diagenetic modification of la th sc distribution is related to the amount of p2o5 present typical la th sc distribution in host shale results when p2o5 values are below 0 5 high la abundance substantially skews la th sc distribution when p2o5 is above 5 0 but when p2o5 is between 0 5 and 5 0 the extent of the effect is unclear oxides of aluminum and other major elements may be useful in recording detrital influence and proximity to the shoreline in phosphorite concretions most of the concretions nearest to shoreline sources of detrital input have both flat ree patterns and elevated values of al2o3 al2o3 fe2o3

dynamics of the stationary anomalies associated with the interannual variability of the midwinter pacific storm track the roles of tropical heating and remote eddy forcing abstract the leading mode of interannual variability of the midwinter pacific storm track is such that the storm track is weaker during the winters when the pacific jet is strong and stronger when the jet is weak in this paper experiments are conducted using a stationary wave model as well as an idealized global circulation model to explore the roles of anomalous tropical heating and eddy fluxes in forcing the observed pacific jet anomalies it is found that enhanced tropical heating over the region 60 e to the date line 25 s to 25 n acts to force a stronger and narrower pacific jet on average tropical heating may account for about one third of the strong jet anomaly but there is significant year to year variability moreover tropical heating does not appear to contribute to the weak jet anomaly much of the pacific jet anomalies are forced by anomalous eddy fluxes by examining the regional contributions from the pacific the atlantic and asia it is found that local eddy feedback over the paci

scale and timing of rare earth element redistribution in the taconian foreland of new england clastic sedimentary rocks deposited on eastern north america in response to the taconian orogeny commonly have sm nd isotope relationships indicating substantial isotope disturbance near or subsequent to the time of sedimentation that may be associated with severe depletion in light rare earth elements lree affected units normanskill formation austin glen and pawlet members frankfort formation and perry mountain formation are widely separated both geographically western new york to western maine and stratigraphically middle ordovician to silurian a model is proposed for the most likely explanation of the observed ree and sm nd isotope relationships involving a two stage process in the first stage ree are redistributed on a mineralogical scale dissolution precipitation on a sample scale often with the involvement of ree enriched trace phases such as apatite and monazite this stage typically takes place during diagenesis but may also take place later during metamorphism and or recent weathering and results in isotope re equilibration on a sample scale the second stage occurs when one or more of these phases is redissolved and ree are transported on large advective scales where lree enriched phases are involved this gives rise to lree depletion in whole rocks the timing of this second stage cannot be constrained from sm nd isotope data and may take place at any time subsequent to the isotope re equilibration such complex histories of ree redistribution may result in serious errors in estimating nd model ages but not in estimating the nd isotope composition at the age of sedimentation thus sm nd ratios even of unmetamorphosed sedimentary rocks have to be carefully evaluated before the calculation of depleted mantle model ages for the provenance

recognising different sediment provenances within a passive margin setting towards characterising a sediment source to the west of the british late carboniferous sedimentary basins to investigate whether sediments with subtly different provenances could be recognised within a passive margin setting samples were taken from westphalian sedimentary rocks of the pennine basin south wales coalfield culm basin of britain and from northern ireland although previous work has shown that 3 major source areas were responsible for the infill of the pennine basin this study is restricted to sediments believed to have been derived from the west their nominally similar western provenance was confirmed using sm nd isotope techniques and their deposition in a passive margin setting was established using elemental discrimination diagrams while the overall sediment provenance may have been from the west the trace element geochemistry indicates that at least two major sediment pathways can be distinguished plots of eu eu gdn ybn along with ternary plots of cr v ti zr gdn ybn or sc cr suggest different source areas for the culm basin and the south wales coalfield in the culm basin the cr v ratio generally exceeds 1 25 with a small eu anomaly and a low gdn ybn ratio the cr v ratio is less than 1 25 in the south wales with a larger eu ratio and a higher gdn ybn than the culm basin significant separation of the culm basin and the south wales coalfield during the early westphalian by the bristol channel bray fault may have been a factor contributing to the provenance differences late carboniferous dextral displacement along this fault brought these basins into close juxtaposition and it is unlikely that the bristol channel landmass formed a common source area for these two basins

storm track organization and variability in a simplified atmospheric global circulation model a storm track is simulated in a coarse resolution multilevel primitive equation model with linear surface friction and heating terms a restoration temperature distribution consisting of a dipole embedded in a zonally symmetric profile forces the model to simulate the surface heating three simulations each with a different dipole orientation are performed to test the sensitivity of storm track organization to the external forcing field the climatological time mean circulation and the transient disturbances of the reference simulation agree well with observations of northern hemisphere wintertime storm tracks local energetics show that baroclinic instability is responsible for the enhanced eddy kinetic energy downstream of the jet and the downstream end of the storm track results from the barotropic conversions of eddy kinetic energy to the time mean flow low frequency fluctuations with a period of about 50 days associated with a retrograding large scale wave pattern are identified by a complex empirical orthogonal function analysis of the vertically averaged stream function a composite life cycle of the low frequency variability reveals the growth and decay of a blocking anticyclone downstream of the storm track a cyclogenesis initiated by an eastward propagating wave train is observed a few days before the amplitude of the low frequency anomaly attains its peak the net forcing of the high frequency eddies contributes to the growth and decay of the blocking anticyclone the results suggest that the occurrence of the blocking like event is part of the storm track dynamics

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

formation of authigenic monazite ce to monazite nd from upper carboniferous graywackes of the drahany upland roles of the chemical composition of host rock and burial temperature abstract irregular aggregates of monazite ce to monazite nd up to 150 m in diameter have been found in graywackes from the protivanov formation drahany upland czech republic monazite aggregates enclose a variety of detrital and authigenic minerals textural evidences suggest that they are of authigenic origin and grew during very low grade metamorphism at a maximum temperature 200 300 c in relation to a deep burial rarely they enclose relics of detrital monazite with a chemical composition typical for high grade monazite intensive fluid related ree remobilization occurred in relation to this very low grade metamorphism authigenic monazite appears to form only in ca poor rocks in ca rich graywackes which underwent the same low temperature metamorphic overprint authigenic synchysite ce or parisite ce are common instead in the overlaying rozstani and myslejovice formations t 150 200 c remobilization of rees was low and authigenic monazite did not form even in the ca poor graywackes authigenic monazite shows low concentrations of th u ca y hree and a low eu anomaly the central parts of the aggregates are enriched in nd mree whereas the outer parts are enriched in la and ce zoning pattern suggests an evolution in fluid chemistry during diagenesis very low grade metamorphism or it relates to different solubility of the individual ree phosphates the major source of rees in the pore fluids are probably detrital minerals mainly monazite other minor sources of rees probably include fe oxide hydroxide and or clay minerals which could have contributed to the nd mree rich cores in the authigenic monazite

control of 36cl production in carbonaceous shales by phosphate minerals abstract when using 36cl to date very old groundwater in regional aquifer systems knowledge of the subsurface 36cl input into the aquifer system is essential although 36cl can be produced through nuclear reactions in the subsurface in many situations the input of 36cl into sedimentary aquifer systems by this avenue of production can be neglected this is a valid assumption when investigating long flowpath groundwater systems composed of sandstones limestones and shales of typical composition these rock types are not sufficiently enriched in radioactive elements to produce significant 36cl in the deep subsurface carbonaceous shales on the other hand can concentrate the radioactive elements necessary to produce significant 36cl in the deep subsurface chlorine 36 ratios 36cl cl for a suite of late devonian and pennsylvanian carbonaceous shales were calculated from bulk rock chemistry as well as measured using accelerator mass spectrometry the poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm an assumption that was not satisfied by the carbonaceous shales in these shales organic matter clay minerals and accessory minerals are heterogeneously distributed and are physically distinct on a micron order scale although organic matter and clay minerals constitute the overwhelming bulk of the shales it is the phosphate minerals that are most important in enhancing and suppressing 36cl production minerals such as apatite and carbonate apatite francolite by including uranium rare earth elements rees and halogens have an important impact on both neutron production and thermal neutron absorption by incorporating both uranium and fluorine phosphate minerals act as neutron production centers in the shale increasing the probability of 36cl production by incorporating rees and chlorine phosphate minerals also act to shield 35cl from the thermal neutron flux effectively suppressing the production of 36cl to reconcile the measured 36cl ratios with the ratios calculated assuming chemical homogeneity the shales were artificially split into three fractions organic clay mineral and phosphate mineral neutron production was calculated separately for each fraction and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36cl ratio than the organic or clay mineral fractions by varying the uranium and chlorine contents in the phosphate fraction a new heterogeneous 36cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales when using rock chemistry to calculate the 36cl ratio rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption in this manner a more accurate heterogeneous 36cl ratio can be calculated for the rock as a whole

multi proxy analysis of organic matter accumulation in the upper ordovician lower silurian black shale on the upper yangtze platform south china abstract there is no doubt that organic matter plays an important role in shale gas accumulation and storage thus successful evaluation and production strategies of organic rich shale deposits require an understanding of the range of factors that contribute to the accumulation and preservation of organic matter in these deposits this paper reports results of a multi faceted study of two ordovician silurian transition sections of the upper yangtze platform of south china organic and inorganic geochemical data are used to reconstruct paleoenvironmental changes across this critical interval of earth history and to identify those factors that were most important to organic matter accumulation deposition of organic rich shale of the katian lower wufeng formation was favored by rising sea level and diminished clastic sediment content black shale of the upper wufeng preceded hirnantian glaciation whereas the overlying lower longmaxi formation accumulated in association with a post glacial rise of sea level as well as the peak of caledonian tectonism the carbonaceous deposits appear to reflect the combined effects of elevated primary productivity as suggested by si al and ti al ratios especially in the upper wufeng and consequent depletion of water column oxygen preservation consideration of the relationships of redox sensitive trace element concentrations and total organic carbon content suggest that bottom water conditions fluctuated between anoxic and euxinic during this period perhaps related to rapid oscillations of sea level moreover the basin appears to have remained connected with the global ocean in spite of caledonian uplift of bordering areas thus black shale sedimentation on the upper yangtze platform at the ordovician silurian boundary reflects the interplay of climate change and tectonism and their influences on sea level clastic sediment content and paleo productivity