coupled re os and u pb geochronology of the tonian chuar group grand canyon well preserved strata of the late tonian chuar group exposed in the grand canyon host fossil evidence for the development of eukaryotic predation the presence of unique biomarkers and large changes in c s and mo isotope chemostratigraphy despite the importance of this critical succession few radioisotopic age constraints are available to place these records into a global context here we couple high precision u pb chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims on zircon crystals with the rhenium osmium re os sedimentary and sulfide geochronometer to refine the temporal framework of this pivotal interval of earth history zircons recovered from a tuff within the uppermost walcott member of the kwagunt formation yield a weighted mean 206pb 238u age of 729 0 0 9 ma mean square of weighted deviates mswd 0 86 differing significantly from the previous air abrasion upper intercept age of 742 6 ma on zircons from this same horizon organic rich carbonates from the carbon canyon member of the galeros formation yield a model 1 re os age of 757 0 6 8 ma mswd 0 47 n 8 and an initial os isotope 187os 188os osi composition of 1 13 0 02 the radiogenic osi value from this horizon suggests that the basin was restricted from the open ocean during deposition of the carbon canyon member in agreement with sedimentological and stratigraphic data the re os geochronology of marcasite fes2 nodules from the awatubi member of the kwagunt formation yield a model 1 age of 751 0 7 6 ma mswd 0 37 n 5 with an osi of 0 44 0 01 this re os date is interpreted to constrain the growth of the marcasite nodules in the awatubi member during deposition the formation of sulfides and the less radiogenic osi value are consistent with an influx of sulfate laden seawater to the basin during deposition of the kwagunt formation attempts to apply the re os geochronometer to the walcott and tanner members of the chuar group failed to yield meaningful ages despite elevated re enrichments 20 ng g the re os data from these units yielded negative osi values which suggest disturbance to the re os system the low os abundances typically 100 pg g relative to the amount expected based on the elevated re abundances suggest leaching of os due to oxidative weathering on geologically recent time scales finally the carbon canyon member provides a useful case study for quantifying how input uncertainties in the re os geochronometer propagate into the resulting age uncertainty and we discuss the protocols that will yield the best improvement in age precision for future studies the u pb and re os geochronology presented here illustrates the power of coupling these systems and the importance of recent improvements in both methods our analysis suggests that for our data the most efficient way of reducing uncertainties in the presented re os dates is through improved precision of measured os values

re os geochronology of the lacustrine green river formation insights into direct depositional dating of lacustrine successions re os systematics and paleocontinental weathering abstract lacustrine sedimentary successions provide exceptionally high resolution records of continental geological processes responding to tectonic climatic and magmatic influences these successions are therefore essential for correlating geological and climatic phenomena across continents and furthermore the globe producing accurate geochronological frameworks within lacustrine strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable tuff horizons the rhenium osmium re os geochronometer is a well established tool for determining precise and accurate depositional ages of marine organic rich rocks lake systems with stratified water columns are predisposed to the preservation of organic rich rocks and thus should permit direct re os geochronology of lacustrine strata we present re os systematics from one of the world s best documented lacustrine systems the eocene green river formation providing accurate re os depositional dates that are supported by ar ar and u pb ages of intercalated tuff horizons precision of the green river formation re os dates is controlled by the variation in initial 187 os 188 os and the range of 187 re 188 os ratios as also documented in marine systems controls on uptake and fractionation of re and os are considered to relate mainly to depositional setting and the type of organic matter deposited with the need to further understand the chelating precursors of re and os in organic matter highlighted in addition to geochronology the re os data records the 187 os 188 os composition of lake water 1 41 1 54 at the time of deposition giving an insight into continental runoff derived from weathering of the geological hinterland of the green river formation such insights enable us to evaluate fluctuations in continental climatic tectonic and magmatic processes and provide the ability for chemostratigraphic correlation combined with direct depositional dates furthermore initial 187 os 188 os values can be used as a diagnostic tool to distinguish between lacustrine and marine depositional settings when compared to known oceanic 187 os 188 os values

geometry mechanisms and significance of extensional folds from examples in the rocky mountain basin and range province u s a abstract geologic mapping and structural analysis in paleogene half graben of idaho and montana have revealed over 70 extensional folds that form orthogonal sets with mostly ne and se trending axes on a regional scale they parallel or lie perpendicular to the strikes of the largest normal faults transverse folds at a high angle to the fault and folds oblique to the fault comprise more than half of the folds and reflect the highly three dimensional nature of the bulk strain detailed geometric analysis of 15 folds in the salmon horse prairie and medicine lodge basins shows that they typically have an upright to steeply inclined bisecting surface an interlimb angle of 141 and a plunge of 19 based on our synthesis of the eight common mechanisms of extensional folding and their distinguishing characteristics we were able to determine how some of the investigated folds formed fault bend folding above both fault parallel and fault perpendicular bends in the underlying normal fault produced most of the folds in the study area but displacement gradients along normal faults fault drag isostatic adjustments and transtension were also factors in the deformation most of the compound folds which result from more than one mechanism of folding are oblique to all adjacent normal faults recognition of such extensional folds is critical because they might be misinterpreted as contractional structures they influence sediment thickness patterns and dispersal in rift basins and may control the migration and trapping of petroleum and groundwater resources

the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

is the marine osmium isotope record a probe for co2 release from sedimentary rocks abstract the marine osmium os isotope composition shows some significant variability during the past 250 000 yr which also correlates with climate sensitive proxies e g oxygen isotopes this correlation led to the assumption that the marine os may in part contain information about past changes of continental weathering as a direct response to large scale events such as northern hemisphere glaciation deglaciation cycles here we test this hypothesis by analyzing marine os isotope records applying an inverse modeling approach with a particular focus on variable weathering rates of os rich lithologies such as organic rich and sulfide rich sedimentary rocks assuming loess represents the os isotope composition of average continental silicate crust weathering thereof would produce an os isotope composition that is close to the modern day seawater value therefore silicate weathering is unlikely to exert any significant control on the marine os isotope composition instead the isotopic variability is thus more likely to be controlled by weathering of rock types enriched in os and with an isotope composition distinct from silicates and seawater weathering of these os rich lithologies is closely linked to high rates of physical erosion and is thus expected to show a strong response to large scale rock grinding glaciation events by combining a model of variable weathering rates to an os cycle model we present a new mechanistic model that is able to explain the late pleistocene marine os isotope variability and we propose that this variability is best explained by a changing continental os fluxes derived from the dissolution of aforementioned os rich lithologies the weathering of such rocks promotes a set of weathering reactions that releases co 2 into the atmosphere and we contend that the marine os isotope record may be suited to gauge relative changes in the magnitude of these processes the modeling results presented here suggest that variable weathering rates of organic rich sedimentary deposits could play an important role in the long term atmospheric co 2 budget and the interplay with co 2 consumption by silicate weathering

petroleum source rock identification of united kingdom atlantic margin oil fields and the western canadian oil sands using platinum palladium osmium and rhenium implications for global petroleum systems this study demonstrates that petroleum and source rocks are enriched in pt and pd to the ppb level and that the 187os 188os composition coupled with the pt pd value permits the fingerprinting of petroleum to its source oils from the united kingdom atlantic margin sourced from the upper jurassic kimmeridge clay fm as well as source rock samples have been analysed for pt and pd when the pt pd value is compared with 187os 188os calculated at the time of oil generation osg the values from both the known source and the oils are similar demonstrating that they can be used as an oil to source fingerprinting tool this inorganic petroleum fingerprinting tool is particularly important in heavily biodegraded petroleum systems where traditional fingerprinting techniques e g biomarkers are severely hampered e g the world s largest oil sand deposit the west canadian oil sands wcos this has caused the source of the wcos to be hotly debated with no present day consensus between inputs from potential source units e g exshaw and gordondale fms 187os 188os and pt pd fingerprinting of the oil sands shows that the majority of the petroleum have similar 187os 188os and pt pd values supporting the hypothesis of one principal source analysis of the potential source rocks establishes that the principal source of the oil sands to be from the jurassic gordondale fm with a minor exshaw fm input thus the combination of previously pioneered re os petroleum geochronology with 187os 188os and pt pd values of petroleum permits both a temporal and spatial understanding of petroleum systems

a baseline survey of the distribution and origin of platinum group elements in contemporary fluvial sediments of the kentish stour england the extensive anthropogenic use of the platinum group elements pge ru rh pd os ir and pt is the main factor responsible for the widespread dispersion of these elements throughout the environment significant quantities of the pge enter fluvial systems via road runoff storm drains and wastewater and sewage treatment systems and may accumulate in fluvial sediments by physical and chemical processes a baseline survey of contemporary fluvial sediments in the kentish stour river east kent england has been undertaken to document the sources and distribution of anthropogenic pge in an attempt to constrain some of the physical and chemical parameters that may influence the distribution of these elements the geology of the catchment of the kentish stour is dominated by carbonate and silicate sedimentary rocks and the river passes through urban and rural land and receives inputs of waste from sewage works nine sedimentary rocks 4 motorway runoff sediments and 22 river sediments were analysed for pge by nis fire assay preconcentration and icp ms the highest element abundances occur in the motorway runoff sediments maximum total pge content of 55 ng g whilst the lowest values were recorded in the sedimentary rocks where some samples contain pge at concentrations below the limit of detection the total pge content of the river sediments ranged from 0 4 to 10 8 ng g the distribution and variation in concentrations and ratios of the pge in the contemporary fluvial sediments of the kentish stour correspond strongly with land use changes urban versus rural and with points of discharge from sewage works the absence of a pure catalytic converter signature in the river sediments however indicates that source signatures may be mixed in sewage works or that pge may chemically fractionate in the fluvial environment

effects of black shale weathering on the mobility of rhenium and platinum group elements radiogenic os from the continents dominates the late cenozoic marine os budget a variety of proposed radiogenic sources includes organic rich sediments precambrian shields and re rich sulfides identifying the dominant sources of radiogenic os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of co 2 whereas weathering of organic matter acts as a source here we investigate the effects of black shale weathering on the integrity of the re os isotope system and release of re and platinum group elements time correlative pairs of fresh drill core and weathered outcrop black shales of late ordovician age utica shale magnafacies quebec were analyzed for re os ir pt and pd as well as total s n and c as c carb and c org the results indicate that 25 64 of the initial re budget 45 90 of the os budget 14 65 of the ir budget 60 77 of the pt budget 69 86 of the pd budget and 44 96 of the c org budget are lost during weathering we use positive correlations of os pt and pd with c org and n to calculate the respective platinum group element concentrations in the unweathered organic matter end member as 3 ng g os 9 ng g pt and 11 24 ng g pd although black shales make up

re os depositional ages and seawater os estimates for the frasnian famennian boundary implications for weathering rates land plant evolution and extinction mechanisms four toc rich shale intervals spanning the frasnian famennian f f boundary were recovered in a drillcore west valley nx 1 from western new york usa and radiometrically dated using re os two of the black shale intervals wvc785 from 2 9 m below and wvc754 from 6 4 m above the f f boundary respectively yielded statistically overlapping ages with uncertainties of 1 1 an interpolated age and associated graphically determined uncertainty of 372 4 3 8 ma provides new absolute age constraints on the f f boundary this date is 4 1 ma younger than the latest proposed f f boundary age of 376 1 ma obtained by interpolation of u pb dates from volcanic zircon kaufmann b 2006 calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy earth science reviews 76 175 190 and within uncertainty of the international commission on stratigraphy accepted date of 374 5 2 6 ma a third date from sample wvc802 8 2 m beneath the f f boundary yielded an imprecise age of 357 23 ma owing in part to a limited re os range the initial 187os 188os 0 45 to 0 47 reflecting contemporaneous seawater os values are low but similar to the value of 0 42 reported for the exshaw fm canada at the devonian mississippian boundary ca 361 ma selby d creaser r a 2005 direct radiometric dating of the devonian mississippian time scale boundary using the re os black shale geochronometer geology 33 545 548 this may suggest fairly constant and low global continental weathering rates during the late devonian although in view of the short residence time of os in seawater 1 4 104 yr further measurements are needed to assess potential short term variation in seawater os ratios owing to low os and re abundances at the f f boundary our data are inconsistent with long term volcanism and bolide impact as potential late devonian mass extinction mechanisms in addition the frasnian famennian ocean appears to have been depleted with respect to re possibly indicating an exhaustion of the re seawater reservoir owing to high burial rates of redox sensitive elements under dysoxic anoxic conditions leading up to the f f boundary

temporal record of osmium concentrations and 187os 188os in organic rich mudrocks implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer the final publication is available at elsevier via https doi org 10 1016 j gca 2017 06 046 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

the duration of ordinary chondrite metamorphism inferred from tungsten microdistribution in metal abstract precise ratios of w and re relative to ir determined by laser ablation icp ms reveal that matrix metal in equilibrated ordinary chondrites eoc exhibits a correlated variation of these ratios in unequilibrated ordinary chondrites uoc the w ir ratio varies by over two orders of magnitude w ir 0 003 0 6 and shows no correlation with any other siderophile element most matrix metal in uoc is depleted in w relative to metal in eoc thus w must enter metal during metamorphism the correlation between w ir and re ir is evident in type 4 chondrites this implies that the abundance and isotopic composition of w is set in ordinary chondrite metal by petrologic type 4 and that the reductant must be exhausted to limit further isotopic exchange as indicated by the 182 hf 182 w ages of ordinary chondrite metal lee and halliday science 274 1996 1876 1879 this offers a means of dating the onset of metamorphic heating of oc parent bodies a discrepancy in ages between 182 hf 182 w lee and halliday science 274 1996 1876 1879 and 207 pb 206 pb gopel et al earth planet sci lett 121 1994 153 171 or 129 i 129 xe brazzle et al geochim cosmochim acta 63 1999 739 760 dating is real and measures the interval of metamorphism the time difference between reduction of w during the onset of heating and isotopic closure of pb or xe by cooling e g t m 2 12 myr for h chondrites the 187 re 187 os and 182 hf 182 w ages are set by the same process metamorphic equilibration establishing an important link between an absolute chronometer t 1 2 187 re 41 6 billion years and a short lived radioisotope system t 1 2 182 hf 9 myr

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

tracking millennial scale holocene glacial advance and retreat using osmium isotopes insights from the greenland ice sheet high resolution os isotope stratigraphy can aid in reconstructing pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine os residence time this paper presents new os isotope data from ocean cores adjacent to the west greenland ice sheet that have excellent chronological controls cores msm 520 and da00 06 represent distal to proximal sites adjacent to two west greenland ice streams core msm 520 has a steadily decreasing os signal over the last 10 kyr 187os 188os 1 35 0 81 in contrast os isotopes from core da00 06 proximal to the calving front of jakobshavn isbrae highlight four stages of ice stream retreat and advance over the past 10 kyr 187os 188os 2 31 1 68 2 09 1 47 our high resolution chemostratigraphic records provide vital benchmarks for ice sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change variations in os isotope composition from sediment and macro algae seaweed sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater os isotope composition further these findings demonstrate that the residence time of os is shorter than previous estimates of 104 yr

different crustal sources for au rich and au poor ores of the grasberg cu au porphyry deposit abstract the grasberg is a porphyry copper deposit that is crosscut by a second stage mineralization which is greatly enriched in gold sulfides from the porphyry type event yield a 2 9 0 3 ma re os isochron that agrees with published geochronology the initial 187os 188os ratio of the isochron is 0 56 0 02 and implies a significant crustal component for the source of os and by inference the other base metals the samples from the crosscutting secondary event do not form an isochron but form a mixing line with the older porphyry style mineralization as one of the end members and a very radiogenic end member possibly shale the initial 187os 188os ratios from samples of the second event range from 0 81 to 1 26 and correlate with gold content the most radiogenic samples have the highest gold the re os isotope data indicate different crustal sources for the ore forming elements at the grasberg cu au deposit and support a model in which gold is derived from sedimentary protoliths that may have been pre enriched by sedimentary processes the gold derived from these sources is concentrated by magmatic hydrothermal systems the requirement of a sedimentary source for gold to produce hydrothermal gold deposits has been debated for decades and this study provides strong support for the model

u pb and re os geochronology of the aptian albian and cenomanian turonian stage boundaries implications for timescale calibration osmium isotope seawater composition and re os systematics in organic rich sediments abstract presented is the first absolute age for the basal albian from the schwicheldt ton member gault formation vohrum germany a 206 pb 238 u age of 113 1 0 3 ma is determined for chemically abraded zircon from a tuff horizon 65 cm above the aptian albian boundary the new u pb age although within uncertainty of the gts 2008 determination 112 1 ma is nominally older the younger gts 2008 basal albian age is obtained from cyclostratigraphy using an 40 ar 39 ar age from the base cenomanian the nominal difference between the gts 2008 age and new basal albian age is consistent with the documented ca 0 65 bias between u pb and 40 ar 39 ar geochronology the new 206 pb 238 u age calls into question a recently published age for the basal albian 106 9 0 4 ma determined from k ar glauconite analysis as well as the k ar age for the gl o international standard rhenium osmium isotope analysis of the basal albian grey clay of the schwicheldt ton member gault formation and basal turonian grey shale of the schwarz weisse wechselfolge hesseltal formation recording oceanic anoxic event 2 yields low and similar 187 re 188 os values 49 167 that are positively correlated with 187 os 188 os values for both sections imprecise re os ages 6 9 2 that overlap the stratigraphic boundary ages are determined aptian albian 108 9 6 2 ma cenomanian turonian 91 5 8 6 ma although the re os data suggest that organic rich sediments other than black shales are potentially amenable for re os geochronology the large uncertainties contrast with that from previous re os organic rich sediment studies the latter show sample sets with a significant spread in 187 re 188 os ratios several hundred units the imprecise re os geochronology presented here relates to the limited spread in the 187 re 188 os values the redox conditions of deposition are suggested to control the 187 re 188 os ratio of an organic rich sediment however trace element and re os data for samples from nw germany and previous re os geochronology studies show no direct relationship between 187 re 188 os values and the redox condition of the water column these results suggest that the fractionation of re and os in organic rich sediments is not controlled by water column redox conditions instead re os fractionation in organic rich sediments may be controlled by sedimentation rate recharge of re and os to the water column and or post deposition mobility of re and os within the sediment the initial os isotope composition of an organic rich sediment is inferred to reflect the seawater composition at the time of deposition for the cenomanian turonian boundary grey shale a seawater os composition of 0 33 0 02 is determined this os isotope composition contrasts with that of the stratotype section at pueblo colorado 0 15 and for those obtained from furlo italy and odp site 1260b 0 5 this data may suggest that the cenomanian turonian ocean was not homogeneous with respect to os suggesting either alternate oceanic circulation or basin dynamics

the osmium isotopic composition of organic rich marine sediments abstract the osmium os concentration and 187 os 186 os ratio of several recent marine organic rich sediment samples from three widely separated sites have been measured os concentrations range from 0 095 to 0 212 ppb and 187 os 186 os ratios range from 8 2 to 8 9 the calculated fraction of hydrogenous os exceeds 78 in all samples thus the 187 os 186 os ratio of these samples reflects os isotopic composition of seawater the small range in measured 187 os 186 os ratio indicates that the os isotopic composition at these sites is fairly homogeneous the large magnitude of the os burial flux at these sites indicates the os burial in association with organic rich sediments is an important sink in the marine cycle of os these data also suggest that ancient organic rich sediments may provide a record of past variations in the os isotopic composition of seawater

geodiversity of high latitude landscapes in northern finland abstract geodiversity is a rather new emerging topic in earth science there is now increased awareness of our need to understand patterns of geodiversity in different landscapes facing global change in this study we systematically inventoried geodiversity and topographical parameters in an area of 285 km 2 in subarctic finland we quantified the spatial variation of geodiversity using four different measures and analysed the relationship between geodiversity and topography using a spatial grid system at a landscape scale the size of the analysis window was 500 500 m the number of different elements of geodiversity total geodiversity varied from 2 to 22 per grid cell the spatial pattern of the total geodiversity geomorphological process variability and geodiversity index were fairly similar whereas of the other geodiversity measures the measure of temporal diversity differed the most topographically the high diversity sites occurred in rather steep sided valleys areas of high geodiversity reflect heterogeneous abiotic conditions where both erosion and accumulation processes play a major role in landscape development the mapping of geodiversity may be indicative not only in the context of geomorphology but also provide a focus for conservation initiatives from a conservation point of view the lack of wider knowledge of the distribution of geodiversity and its relationship to biodiversity hinders the protection of ecologically and geomorphologically valuable regions thus we recommend that further studies focus on 1 quantifying spatial patterns of geodiversity in different regions 2 determining the key drivers that control the variability of geodiversity and 3 exploring the linkage between geodiversity and biodiversity

comprehensive evolution of a petroleum system in absolute time the example of brynhild norwegian north sea abstract petroleum systems are inherently complex comprising multiple components and processes which variably interact in space and time to form petroleum accumulations improved understanding of these complex systems requires a holistic approach of integrating diverse geological geophysical and organic and inorganic geochemical data here we present an applied and comprehensive re os geochronological and geochemical study on the brynhild petroleum system from the norwegian north sea essential components of this system include shale source rocks of the mandal and farsund formations reservoir sandstones of the ula formation and their bitumen extracts and produced brynhild crude oil rock eval trace metal and re os data reveal the excellent oil generation potential of the shaley source rocks high contents of organic matter containing large amounts of type i kerogens and constrain their depositional conditions anoxic bottom waters in a high productivity regime driven by enhanced supply of land derived nutrients seven re os shale ages between 146 and 134 ma are consistent with existing volgian ryazanian age estimates and constrain the initial 187os 188os of the shales to 0 52 in the lowermost farsund formation and 0 75 in the uppermost mandal formation solvent extracted reservoir rocks of the ula formation contain insoluble organic matter with type iii type iv kerogens likely supplied by erosion of older a precise 179 ma re os age with unrealistically low initial 187os 188os coal bearing sediments or organic rich shales the brynhild crude oil has relatively low 187os 188os and a generation age of 44 ma based on an asphaltene only re os isochron maltenes from the brynhild crude oil are isotopically affected by interaction with organic rich source rocks that represent the seal for the brynhild oil field compared with the crude oil bitumen from ula formation sandstones have contrasting re os properties high 187os 188os ratios and young generation ages between 8 and 0 ma based on asphaltene bitumen maltene re os triplets asphaltene only re os regressions and re os model ages for components with extremely high 187re 188os the 44 ma and 8 0 ma re os ages agree well with regional burial models that indicate oil generation from 44 ma to present day a genetic link between crude oil and bitumen is indicated by their similar alkane patterns v and ni contents and v ni and pristane phytane ratios modeling of 187os 188os for individual organic components through time shows that shales of the mandal formation developed 187os 188os ratios that match those of the crude oil and bitumen at 44 ma and 8 ma respectively and therefore confirm the source for both hydrocarbon phases we suggest that bitumen formed during in reservoir mixing of a 44 ma old early mature asphaltene poor oil brynhild crude oil with an 8 ma old asphaltene rich oil

the os isotopic composition of himalayan river bedloads and bedrocks importance of black shales re os data are presented for bedrocks and bedloads of selected rivers from the himalayan range in central nepal and bangladesh these data demonstrate that the os isotopic composition of most of the bedrocks is similar to that of the average continental crust notable exceptions to this are the black shales from the lesser himalaya lh which contain large quantities of radiogenic osmium in the black shales the os is not concentrated in the sulfides and may instead be associated with organic matter bedloads collected from rivers which include lh black shales in their catchment basins have notably high os ratios 187os 188os 3 this radiogenic signature persists into the ganga river in contrast the brahmaputra river is less radiogenic suggesting an ophiolite input in the headwater region simple physical mixtures of lh black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high os ratios observed at the outflow of the range assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture respectively this observation suggests that erosion may not be occurring at steady state in addition mass balance calculations indicate that about 20 of the os and 60 of the re are carried in dissolved form implying that chemical erosion plays an important role in the osmium budget finally the contrast in os isotope ratio between ganga bedloads and bulk sediments in the bengal fan suggests that radiogenic os carried by particulate matter and later remobilized may significantly influence the os composition of seawater

rhenium osmium and molybdenum isotope systematics of black shales from the lower cambrian niutitang formation sw china evidence of a well oxygenated ocean at ca 520 ma abstract the early cambrian was a key period in earth s history and the reconstruction of ancient ocean chemistry on spatial and temporal scales can contribute to a better understanding of events during that period new early cambrian data for re os and mo isotopic compositions and redox sensitive elements rse are reported here for the niutitang formation se chongqin sw china a re os age of 520 30 myr model 3 2 n 21 mswd 62 and a 187os 188os i ratio of 0 79 0 11 were obtained consistent with previously reported data for equivalent strata from other areas separate regression of samples with 187os 188os i of 0 72 0 79 and 0 81 0 89 produce more precise ages of 520 1 9 5 myr model1 2 n 7 mswd 1 0 and 513 10 myr model 1 2 n 8 mswd 0 96 respectively suggesting heterogeneity in the primary source of os as the dominant cause of scatter and uncertainty high initial 187os 188os of 0 79 0 11 may indicate a high os input from oxidative weathering of upper continental crust for early cambrian ocean based on rse data such as mo u v enrichment and ni co v cr v v ni moef uef re mo ratios two geochemically distinct zones upper and lower can be delineated in the sedimentary sequence as reflected in drillcore sections the upper section n 9 is characterized by low total organic carbon toc contents mean 1 8 1 5 wt low rse contents mo 0 008 0 006 10 3 g g v 0 22 0 15 10 3 g g u 0 008 0 004 10 3 g g and low v cr 2 0 1 7 ni co 5 9 3 5 moef uef 2 6 1 8 and mo toc 6 0 3 9 ratios in contrast the lower core section n 13 is characterized by high toc contents 4 4 2 2 wt high rse contents mo 0 10 0 08 10 3 g g v 1 0 1 0 10 3 g g u 0 05 0 04 10 3 g g high v cr 6 5 ni co 24 14 moef uef 6 3 2 2 and mo toc 21 9 ratios uncertainties are 1sd here significantly decreasing trends of those redox proxies from lower to upper sections suggest that the depositional conditions evolved from anoxic euxinic to oxic condition all samples display extremely low re mo ratios of 0 2 10 3 1 9 10 3 indicating the absence of intermediate reducing conditions possibly reflecting rapid ocean oxygenation the mo isotopic composition in the sedimentary succession of the yc9 core exhibits a large variation with 98 95mo values of 0 04 2 00 upper section 98 95mo values display an opposite trend to mn content and negative correlation with mo toc ratios indicating mo fractionation associated with adsorption on mn oxides or oxyhydroxides lower section 98 95mo values are positively correlated with mo toc ratios and negatively with re mo ratios suggesting incomplete conversion of molybdates to tetrathiomolybdates under weakly euxinic conditions high 98 95mo of 2 00 and high average mo toc ratios of 21 10 6 g g wt were observed in euxinic shales in the niutitang formation suggesting extensive ocean oxygenation may have taken place at ca 520 ma

variations of the187os 186os ratio of seawater over the past 28 million years as inferred from metalliferous carbonates abstract the os concentration and isotopic composition of metalliferous carbonates deposited on the east pacific rise over the past 28 ma are reported with complimentary sr isotope data variations in the os isotopic composition of these samples are interpreted as a record of past changes in the os isotopic composition of seawater these results are consistent with isotopic analyses of leachable os in pelagic clays which have also been interpreted as a record of the187os 186os ratio of seawater through time 1 the metalliferous carbonate record clearly shows that seawater os and sr isotope systems are partially decoupled from one another over the past 28 ma accelerated weathering of ancient organic rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the187os 186os ratio of seawater over the past 15 ma this rapid increase suggests that the seawater os record can potentially be used as a stratigraphic tool in some neogene marine deposits

isotopic composition of osmium in terrestrial samples determined by accelerator mass spectrometry interest has revived in the rhenium osmium system due to significant advances in detection methods1 4 and because of its use for the identification of extraterrestrial material at the cretaceous tertiary boundary5 another perhaps more important application is its use as a tracer for the origin of crustal material this application is however severely restricted by the very low concentrations typical of crustal rocks we present here the first results for the isotopes 187os 188os and 189os measured in sub p p b parts per 109 level samples by accelerator mass spectrometry ams our first exploratory measurements on extraterrestrial and crustal material with os concentrations between 2 p p m parts per 106 and 0 006 p p b show a detection limit of 0 01 p p b and a precision of better than 10 the 187os 186os ratios measured for samples for the canyon diablo meteorite and from the east clearwater crater in quebec canada were close to 1 typical of extraterrestrial material in contrast ratios in samples from the ries crater in germany were around 10 which is evidence of predominantly crustal osmium in these rocks

relations between hinterland and foreland shortening sevier orogeny central north american cordillera the tectonic relations between foreland and hinterland deformation in noncollisional orogens are critical to understanding the overall development of orogens the classic central cordilleran foreland fold and thrust belt in the united states late jurassic to early tertiary sevier belt and the more internal zones to the west central nevada thrust belt provide data critical to understanding the developmere of internal and external parts of orogens the garden valley thrust system part of the central nevada thnkst belt crops out in south central nevada within a region generally considered to be the hinterland of the jurassic to eocene sevier thrust belt the thrust system consists of at least four principal thrust plates composed of strata as young as pennsylvanian in age that are unconformably overlain by rocks as old as oligocene suggesting that contraction occurred between those times new u pb dates on intrusions that postdate contraction combined with new paleomagnetic data showing significant tilting of one area prior to intrusion suggest that regionally these thrusts were active before 85 100 ma the thrust faults are characterized by long relatively steeply dipping ramps and associated folds that are broad and open to close upright and overturned although now fragmented by cenozoic crustal extension individual thrusts can be correlated from range to range for tens to hundreds of kilometers along strike we correlate the structurally lowest thrust of the garden valley thrust system the golden gate mount irish thrust southward with the gass peak thrust of southern nevada this correlation carries the following regional implications at least some of the slip across jurassic to mid cretaceous foreland thrusts in southern nevada continues northward along the central nevada thrust belt rather than noaheastward into utah this continuation is consistent with age relations which indicate that thrusts in the type sevier belt in central utah are synchronous with or younger than the youngest thrusts in southern nevada this in turn implies that geometrically similar sevier belt thrusts in utah must die out southward before they reach nevada that slip along the southem nevada thrusts is partitioned

can geodiversity be predicted from space abstract identification of geodiversity at regional and national scales with traditional surveying techniques remains a logistically difficult and often financially prohibitive task earth observation data in combination with statistical modeling may provide a unique approach for mapping and analyzing geodiversity cost efficiently in this study the possibility to map geodiversity using digital elevation models dems and remote sensing rs data was scrutinized in finland northern europe at a landscape scale the main methods in the evaluation of spatial prediction ability of geodiversity and the relative contributions of dem and rs data were generalized additive modeling gam and variation partitioning based on the results geodiversity was mainly determined by polygenetic bedrock topography and fluvial activity and correlated most strongly with variables describing high potential energy and topographical heterogeneity the spatial patterns of geodiversity were robustly predicted across the study areas using multivariate gams the higher predictive performance of the dem versus rs based variables was evident across the study areas in conclusion we propose that statistically based spatial prediction offers an opportunity for characterizing geodiversity of a large area in a systematic repeatable and spatially exhaustive manner

molybdenum isotopes in hydrothermal manganese crust from the ryukyu arc system implications for the source of molybdenum abstract a high concentration of molybdenum mo is a striking feature of modern marine hydrothermal manganese mn crusts from both low and high temperature hydrothermal systems however the origin of that mo is poorly constrained in this study we analyzed mo isotopic composition 98 95mo in a mn crust collected from the ryukyu arc system and assessed the possible use of 98 95mo to constrain the origin of mo in hydrothermal mn crusts along with mo isotope analysis we also measured the abundance of major and trace elements and the re os isotopic composition the mn crust sample had a high mn content 42 47 and was low in fe 0 2 0 5 among the manganophile elements co ni cu zn and mo only mo showed high concentrations 550 ppm we also found low contents of os 35 ppt with an isotopic composition of 187os 188os 1 00 these results are consistent with previously reported chemical compositions of hydrothermal mn crusts 98 95mo values in the sample ranged from 0 56 to 0 66 which are 2 7 lighter than the present day seawater 98 95mo but similar to those in modern hydrogenous fe mn crusts and mn nodules although current data do not preclude the possible contribution of hydrothermally derived mo the light 98 95mo values can be explained by isotope fractionation associated with a change in coordination number during the adsorption of mo from seawater onto mn oxides we suggest that the 98 95mo data are useful for constraining the source of mo in hydrothermal mn crusts

zircon and apatite u th he evidence for paleogene and neogene extension in the southern snake range nevada usa despite decades of study the timing rates and magnitude of extension in the basin and range are poorly quantified in some areas this study integrates new zircon and apatite u th he analyses zrnhe and aphe with published thermochronologic data to quantify these extensional parameters in the southern snake range ssr of east central nevada the new zrnhe dates range from 40 7 4 9 ma in the western ssr to 21 0 3 3 ma near the present day trace of the southern snake range decollement ssrd and the aphe dates range from 15 1 2 4 ma in the central ssr to 13 6 0 7 ma closest to the ssrd trace these new and previously published low temperature thermochronologic cooling ages were inverted for the extensional history of the ssr using a bayesian monte carlo method incorporating pecube the posterior extensional histories indicate three significant pulses of extension occurred during the paleogene and neogene 1 50 45 to 38 ma eocene 2 33 30 to 23 ma oligocene and 3 23 20 to 10 8 ma miocene modeled rates of extension were low at 0 5 mm a 1 however more rapid rates possibly occurred during the eocene and the miocene based on posterior histories net cumulative extension from posterior histories is 19 8 to 34 9 km with a mean of 29 7 km about 10 18 km of extension occurred during the eocene and oligocene model results indicate no relationship between extension and magmatism in the ssr our new model results and interpretations also indicate extensional collapse of the nevadaplano initiated prior to 17 ma

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

osmium isotopic evidence against an impact at the frasnian famennian boundary two sections across the frasnian famennian boundary were analyzed for re and os concentrations and 187os 188os ratios to evaluate evidence for a meteoritic input coincident with this boundary and its associated mass extinction these sections are from a siltstone and shale sequence at irish gulf in new york us and a calcareous shale and ferromanganese oxide sequence at la serre in france the irish gulf section with an initial 187os 188os of about 0 49 does not show the characteristic meteoritic os imprint with an 187os 188os of about 0 13 the integrity of the section with regard to re and os retention is indicated by the construction of an isochron with an age of 388 41 ma consistent with independently determined ages for the frasnian famennian boundary although the la serre section with os concentrations as high as 33 ppb and re concentrations ranging from 1 4 to 7 4 ppb might be expected to show excellent evidence for a meteoritic contribution the highly radiogenic isotopic composition 187os 188os 2 42 3 61 instead suggests recent massive re loss or addition of radiogenic os these possibilities prevent the reconstruction of an initial 187os 188os value for the boundary for this site assuming reasonable re concentrations prior to loss the os isotopic composition is inconsistent with a large meteoritic component this inconsistency emphasizes that platinum group element pge concentrations are not reliable indicators of extraterrestrial addition

anoxic sediments an important environment for pge an overview anoxic sediments and metasediments have been recently recognized as important host environments for the platinum group elements pge economically significant pge concentrations have been reported from marine metal rich black shales in china yukon canada and poland these ore bearing horizons are characterized by extremely restricted vertical and sometimes larger horizontal extents they are associated with the evolution of intracontinental rifting structures without any magmatic activity suggesting a possible driving mechanism for mineralization processes complex pge associations including a significant relationship of pd and pt with ni bi se y and also with sb cu co au u and f are suggested using the results of a new statistical evaluation of available geochemical data these occurrences show more common features with other hydrothermal pge deposits the rift volcanic related marine metal rich black shales of the czech republic and finland however display lower pge values the mineralized layers are much thicker with a typically limited horizontal extent showing a close association with volcanic centres pd reveals a strong correlation with ni zn au and v pt exhibits a highly significant link with the cu and mo phases low average nicu ratios and pge au chondrite normalized patterns are similar to those of some magmatic pge deposits hosted in mafic and ultramafic rocks it is very likely that organic matter played an important role in the genesis of pge accumulations in metal rich black shales in both rift and rift volcanic related environments

effects of sample size on the accuracy of geomorphological models abstract commonly the most costly part of geomorphological distribution modelling studies is gathering the data thus guidance for researchers concerning the quantity of field data needed would be extremely practical this paper scrutinises the relationship between the sample size the number of observations varied from 20 to 600 and the predictive ability of the generalized linear model glm generalized additive model gam generalized boosting method gbm and artificial neural network ann in two data settings i e independent and split sample approaches the study was performed using empirical data of periglacial processes from an area of 600 km2 in northernmost finland at grid resolutions of 1 ha 100 100 m and 25 ha 500 500 m a rather sharp increase in the predictive ability of the models was observed when the number of observations increased from 20 to 100 and the level of robust predictions was reached with 200 observations the result indicates that no more than a few hundred observations are needed in geomorphological distribution modelling at a medium scale resolution ca 0 01 1 km2

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

platinum group elements pge and rhenium in marine sediments across the cretaceous tertiary boundary constraints on re pge transport in the marine environment the nature of re platinum group element pge pt pd ir os ru transport in the marine environment was investigated by means of marine sediments at and across the cretaceous tertiary boundary ktb at two hemipelagic sites in europe and two pelagic sites in the north and south pacific a traverse across the ktb in the south pacific pelagic clay core found elevated levels of re pt ir os and ru each of which is approximately symmetrically distributed over a distance of 1 8 m across the ktb the re pge abundance patterns are fractionated from chondritic relative abundances ru pt pd and re contents are slightly subchondritic relative to ir and os is depleted by 95 relative to chondritic ir proportions a similar depletion in os 90 was found in a sample of the pelagic ktb in the north pacific but it is enriched in ru pt pd and re relative to ir the two hemipelagic ktb clays have near chondritic abundance patterns the 1 8 m wide re pge peak in the pelagic south pacific section cannot be reconciled with the fallout of a single impactor indicating that postdepositional redistribution has occurred the elemental profiles appear to fit diffusion profiles although bioturbation could have also played a role if diffusion had occurred over 65 ma the effective diffusivities are 10 13 cm 2 s much smaller than that of soluble cations in pore waters 10 6 cm 2 s the coupling of re and the pges during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances if redistribution was caused by diffusion then the effective diffusivities are the same fractionation of os from ir during the ktb interval must therefore have occurred during aqueous transport in the marine environment distinctly subchondritic os ir ratios throughout the cenozoic in the south pacific core further suggest that fractionation of os from ir in the marine environment is a general process throughout geologic time because most of the inputs of os and ir into the ocean have os ir ratios 1 mass balance calculations show that os and re burial fluxes in pelagic sediments account for only a small fraction of the riverine os 10 and re 0 1 inputs into the oceans in contrast burial of ir in pelagic sediments is similar to the riverine ir input indicating that pelagic sediments are a much larger repository for ir than for os and re if all of the missing os and re is assumed to reside in anoxic sediments in oceanic margins the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes however putting all of the missing os and re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of os at pelagic ktb sites where at most 25 of the k t impactor s os could have passed through estuaries if os is preferentially sequestered in anoxic marine environments it follows that the os ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition there is thus a clear fractionation of os and re from ir in precipitation out of sea water in pelagic sections accordingly it is inferred here that re and os are removed from sea water in anoxic marine depositional regimes

copper zinc chromium and osmium isotopic compositions of the tepla barrandian unit black shales and implications for the composition and oxygenation of the neoproterozoic cambrian ocean abstract two neoproterozoic cambrian shale suites that consist of normal nbs and metal rich hmbs black shales from the tepla barrandian unit bohemian massif czech republic are studied in terms of their cu zn cr and re os isotopic compositions to improve our knowledge of elemental and isotopic mass balance of these elements in earth s oceans in the past and the extent of surface oxygenation at the neoproterozoic cambrian boundary the rock compositions indicate that the inputs of cu and zn have been controlled by variable proportions of metal rich authigenic and low metal terrigenous sources the latter having exceptionally low 65cu and partially 66zn in this respect our data confirm previous studies conclusions that organic rich sediments with high a terrigenous flux play an important role in the sinking of light zn in the oceans and provide new evidence that these types of rocks also represent the currently unidentified burial of very light cu in the ocean the chromium isotopic composition reveals a complex history of cr uptake and fractionation through the dominant cr input from different terrigenous sources with variable 53cr followed by cr fractionation that was controlled by redox states nbs on the other hand mixing and or continuous equilibrium isotopic exchange between seawater and hydrothermal cr was the dominant process for the hmbs the re os contents of the nbs were controlled by hydrogenous components which yield a poorly defined re os age for the least disturbed samples of 555 60 ma indicating an open system behavior while the hmbs re os composition was largely influenced by hydrothermal fluids during deposition the calculated authigenic 65cu which is similar to that in the present day ocean and highly positive 53cr values of the hmbs suggest high levels of surface oxygenation during the neoproterozoic cambrian transition furthermore the authigenic 66zn which is indistinguishable from that in the present day ocean may imply a constant zn isotopic composition of the oceans from the neoproterozoic because of the well balanced cycle of phosphates which were strongly adsorbed by fe hydroxides the radiogenic nature of the initial 187os 188os 0 6 although with a high associated error seems to not confirm previous indications of an abrupt increase of seawater 187os 188os during the late neoproterozoic due to the large scale radiogenic os flux into the ocean

interaction of geomorphic and ecologic features across altitudinal zones in a subarctic landscape abstract vegetation is often considered to stabilize geomorphic processes an increasing abundance of vegetation may cause negative feedbacks within a periglacial system in this study we explored the importance of vegetation on the occurrence of active cryoturbation dominated feature fields in subarctic finland on a landscape scale the vegetation cryoturbation interaction was studied across three altitudinal zones by applying hierarchical partitioning hp and variation partitioning vp methods that overcome collinearity problems in multivariate analysis firstly our results showed that vegetation factors especially the canopy cover of the field layer vegetation and the total above ground biomass were among the most important environmental variables affecting the occurrence of active cryoturbation features moreover vegetation factors were for the most part positively associated with cryoturbation under the predicted global warming the greening of arctic and subarctic regions may therefore decrease and also increase the activity of the periglacial processes in sparsely vegetated terrain secondly our analyses gave contrasting results of the environmental factors of the periglacial processes across altitudinal zones although the relative importance of the vegetation group was rather constant throughout the zones thus we stress the importance of the spatial study setting in geomorphic studies in topographically varying relief we recommend either taking the altitudinal zonation of the landscape into consideration or studying the features within a predetermined zone to decrease misinterpretations in environment process relationships methodologically our results encourage wider applications of partitioning methods in multivariate settings in geomorphology

direct radiometric dating of hydrocarbon deposits using rhenium osmium isotopes rhenium osmium re os data from migrated hydrocarbons establish the timing of petroleum emplacement for the giant oil sand deposits of alberta canada at 112 5 3 million years ago this date does not support models that invoke oil generation and migration for these deposits in the late cretaceous most re os data from a variety of deposits within the giant hydrocarbon system show similar characteristics supporting the notion of a single source for these hydrocarbons the re os data disqualify cretaceous rocks as the primary hydrocarbon source but suggest an origin from older source rocks this approach should be applicable to dating oil deposits worldwide

geochemical evidence for volcanic activity prior to and enhanced terrestrial weathering during the paleocene eocene thermal maximum abstract the re os and major element geochemistry of an expanded gray shale sequence from the central basin in spitsbergen svalbard archipelago norway over the paleocene eocene thermal maximum petm is presented the data suggest that a significant volcanic episode as indicated primarily by a large drop in 187 os 188 os occurred just prior to or coincident with the onset of the petm the distinct geochemistry of the inferred ash component is consistent with the geochemistry of contemporaneous ashes previously sampled in denmark and persists in the sedimentary record for 8 ka based on the substantial size of the 187 os 188 os decrease 187 os 188 os 0 23 the volcanic event must have involved widespread ash deposition in the local catchment the terrestrially deposited ash weathered rapidly shifting the 187 os 188 os of the basin water column to 187 os 188 os to more radiogenic values and depositing clastic materials with higher chemical index of alteration and lower na ti persistently anoxic sedimentary pore fluids interpreted to reflect bottom water anoxia initiated close to the onset of the petm anoxic mainly euxinic conditions persisted for 50 ka ending abruptly 55 77 ma anoxia appears related to enhanced high latitude hydrological cycling and consequent basinal stratification during the petm

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

assessing regional geodiversity the iberian peninsula geodiversity is a landscape characteristic related to the heterogeneity of the physical properties of the earth surface in this work we quantify and compare geodiversity in several geodynamic zones of the iberian peninsula for this purpose we have developed a geographic information system gis procedure to carry out a regional terrain classification based on geodiversity factors a classification process helped to produce a morphometric map 10 classes a morphoclimatic map five classes and a geological map 15 classes these three maps were combined using an overlay operation union to obtain the final terrain classification 419 classes which was then applied to calculate diversity landscape indices the latter were calculated using common landscape diversity indices patch richness density shannon s diversity index shannon s evenness index simpson s diversity index and simpson s evenness index provided by fragstats free software these indices were calculated for the whole landscape of the main iberian geological regions thus revealing a close relationship between some index values and the geological and geomorphological characteristics the highest diversity values are associated with alpine collisional orogens and reactivated chains of the precambrian palaeozoic massif intraplate orogen with sedimentary cover characterized by extensive planation surfaces have lower values mesozoic areas with no significant tectonic deformation and cenozoic basins are characterized by the lowest diversity values amongst the latter the major diversity is associated with the most dissected basins which also present higher morphoclimatic variety though depending on the chosen scale and the landscape classification criteria these indices provide an objective assessment of the regional geodiversity of iberia copyright 2009 john wiley sons ltd

gis and sda applications in geomorphology abstract this special issue of geomorphology consists mainly of selected papers from the s15 session gis and sda applications in geomorphology at the 6th international conference on geomorphology held in zaragoza spain in september 2005 for this session 53 abstracts from europe asia the americas africa and oceania were submitted and 18 oral communications and 35 posters were presented the session provided an opportunity to overview discuss and evaluate new advances of gis geographical information systems and sda spatial data analysis applications in the field of geomorphology eight of the manuscripts submitted for the publication call for this special issue survived the review process and two other invited contributions together form this special issue with 10 papers

re os isotope systematics in black shales from the lesser himalaya their chronology and role in the 187os 188os evolution of seawater abstract re and os abundances and os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines maldeota and durmala in the lesser himalaya the re and os concentrations in these samples exhibit wide range 0 2 to 264 ng g and 0 02 to 13 5 ng g respectively with a mean re os of 25 the 187 os 188 os of these samples also show a broad range 1 02 to 11 6 with many of them far more radiogenic than the currently eroding continental crust the black shales from the maldeota and durmala mines collected a few meters above the krol tal pc c boundary and occurring in the same stratigraphic horizon yield 187 re 187 os isochron ages of 554 16 and 552 22 ma respectively consistent with fossil evidences and those assigned for the pc c boundary at various other locations these results indicate closed system behaviour of re and os in these mine samples and reaffirm the validity of 187 re 187 os pair to date organic rich sediments the age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary re os age of 839 138 ma for black shales from theog collected from the inner belt these initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt however more analyses of black shales are needed to confirm this the role of weathering black shales from the himalaya in contributing to the os isotope evolution of seawater over the past 25 ma was assessed using a simple budget model for seawater os and assuming values for os fluxes and 187 os 188 os based on the available limited data on os concentration and its 187 os 188 os in rivers and oceans these calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187 os 188 os over the past 16 ma is difficult to satisfy by varying only the os flux from htp rivers 187 os 188 os kept constant at 1 324 or their 187 os 188 os 188 os flux constant at today s value 131 moles yr the requirements to balance os isotope budget in ocean through weathering of black shales however is easier to accommodate if both the os flux from htp himalayan tibetan plateau rivers and their 187 os 188 os are allowed to vary measurements of os abundance in htp rivers and its isotopic composition are needed to test the validity of the model results

re os age and depositional environment for black shales from the cambrian ordovician boundary green point western newfoundland chemical and isotopic signatures for black shales serve as potential proxies for reconstruction of paleoenvironmental conditions here we bring rock eval major and trace element and re os isotopic data together to examine the environmental record at the cambrian ordovician global stratotype section and point gssp at green point in western newfoundland canada the green point shales are oil mature and contain type ii organic material of marine origin a re os isochron for the shales provides the first radiometric age for shale deposition at the gssp at 484 16 ma with an initial 187os 188os ratio of 0 74 0 05 model 3 age mswd 21 n 13 2 uncertainties factor analysis of the geochemical data set shows association of most trace elements with total organic carbon toc and s contents ensuring an authigenic origin for most elements and hence their validity for evaluating the paleo redox state relatively high enrichment factors for redox sensitive elements e g re u and mo compared to average shale but comparatively low enrichment compared to modern black sea sediments suggest deposition in anoxic but not euxinic waters comparison of lower ordovician shale geochemistry data sets at a global scale leads us to suggest that anoxic conditions and warm oceanic regimes were restricted to the margins of laurentia and baltica whereas depositional basins with colder waters e g avalonia and gondwana were less reducing these outcomes underscore the important role of paleogeography in regulating oceanic conditions and marine life

an osmium based method for assessing the source of dissolved rhenium and molybdenum to archean seawater abstract authigenic enrichments of re and mo in 2 7 2 5 ga organic rich mudrocks orm indicate that dissolved re and mo were present in late archean seawater however it can be difficult to determine if the dissolved re and mo were sourced from oxidative crustal weathering or magmatic hydrothermal extraterrestrial mhe inputs comparison of re mo and 192 os non radiogenic os isotope concentrations and initial 187 os 188 os isotope compositions from re os isochron regressions of orm can shed insight on the source of re and mo to archean seawater seawater 187 os 188 os reflects the relative contributions of radiogenic crustal versus unradiogenic mhe os inputs to seawater during the phanerozoic transient increases in magmatic hydrothermal activity marked by unradiogenic 187 os 188 os excursions and higher 192 os concentrations in orm are accompanied in some cases by higher re concentrations these unradiogenic os sources could thus have played a greater role in the archean marine re and possibly mo budget given that the riverine re and mo flux at that time was likely smaller than the phanerozoic flux hence a positive correlation between re mo and 192 os concentrations in archean orm that yields unradiogenic initial 187 os 188 os may reflect a mhe origin for dissolved re and mo in the overlying paleo seawater local oxidative weathering in the presence of photosynthetic o 2 of mafic ultramafic rocks and crustal sulfide minerals with low re os ratios is an alternative explanation but the two scenarios cannot be readily distinguished on the basis of initial 187 os 188 os by contrast an initial 187 os 188 os from archean orm that is statistically higher than the mhe baseline of 0 10 0 11 points to oxidative mobilization of re os and mo from crustal sulfide minerals rhenium and mo concentrations that are negatively correlated with 192 os concentrations in archean orm yielding unradiogenic initial 187 os 188 os suggests that some re and mo were derived from oxidative weathering such negative correlations may reflect an increased marine os sink adsorption to oxide minerals during a mild increase in local environmental o 2 levels these concepts may help trace the onset of photosynthetic o 2 production and accumulation along archean ocean margins

evaluation of the rhenium osmium geochronometer in the phosphoria petroleum system bighorn basin of wyoming and montana usa rhenium osmium re os geochronometry is applied to crude oils derived from the permian phosphoria formation of the bighorn basin in wyoming and montana to determine whether the radiogenic age reflects the timing of petroleum generation timing of migration age of the source rock or the timing of thermochemical sulfate reduction tsr the oils selected for this study are interpreted to be derived from the meade peak phosphatic shale and retort phosphatic shale members of the phosphoria formation based on oil oil and oil source rock correlations utilizing bulk properties elemental composition 13c and 34s values and biomarker distributions the 34s values of the oils range from 6 2 to 5 7 with oils heavier than 2 interpreted to be indicative of tsr the re and os isotope data of the phosphoria oils plot in two general trends 1 the main trend n 15 oils yielding a triassic age 239 43 ma with an initial 187os 188os value of 0 85 0 42 and a mean square weighted deviation mswd of 1596 and 2 the torchlight trend n 4 oils yielding a miocene age 9 24 0 39 ma with an initial 187os 188os value of 1 88 0 01 and a mswd of 0 05 the scatter high mswd in the main trend regression is due in part to tsr in reservoirs along the eastern margin of the basin excluding oils that have experienced tsr the regression is significantly improved yielding an age of 211 21 ma with a mswd of 148 this revised age is consistent with some studies that have proposed late triassic as the beginning of phosphoria oil generation and migration and does not seem to reflect the source rock age permian or the timing of re migration late cretaceous to eocene associated with the laramide orogeny the low precision of the revised regression 21 ma is not unexpected for this oil family given the long duration of generation from a large geographic area of mature phosphoria source rock and the possible range in the initial 187os 188os values of the meade peak and retort source units effects of re migration may have contributed to the scatter but thermal cracking and biodegradation likely have had minimal or no effect on the main trend regression the four phosphoria sourced oils from torchlight and lamb fields yield a precise miocene age re os isochron that may reflect the end of tsr in the reservoir due to cooling below a threshold temperature in the last 10 m y from uplift and erosion of overlying rocks the mechanism for the formation of a re os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187re 188os values from an oil family

pge re os and mo isotope systematics in archean and early proterozoic sedimentary systems as proxies for redox conditions of the early earth abstract re os data and pge concentrations as well as mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the barberton greenstone belt south africa fig tree and moodies groups 3 25 3 15 ga the belingwe greenstone belt zimbabwe manjeri formation ca 2 7 ga and shales from the witwatersrand ventersdorp and transvaal supergroups south africa ranging from 2 95 to 2 2 ga moderately oxidizing conditions are required to mobilize re and mo in the environment mo fractionation only occurs in solution and these parameters thus have potential use as paleoredox proxies for the early earth pge re abundance patterns of barberton greenstone belt sediments are uniform and very similar in shape to those of komatiites this indicates 1 that the pge came from a source of predominantly ultramafic composition and 2 that pge were transported and deposited essentially in particulate form sediments from the younger belingwe greenstone belt show more fractionated pge re patterns and have re os ratios 10 to 100 higher than those of barberton sediments their pge abundance patterns and re os ratios are intermediate between those of the mid archean shales and neoproterozoic to recent black shales they reflect scavenging of re from solution in the sedimentary environment 98 95 mo values of black shales of all ages correlate with their concentrations the barberton greenstone belt samples have 1 3 ppm mo similar to a granitoid basaltic source this mo has 98 95 mo between 1 9 and 2 4 relative to present day mean ocean water molybdenum momo and is thus not isotopically fractionated relative to such a source similar to the pge this indicates transport in solid form sediments from the belingwe greenstone belt show in part enhanced mo concentrations up to 6 ppm and mo isotope fractionation 98 95 mo up to 1 4 relative to momo the combined pge re and mo data show mainly reducing conditions in the mid archean and suggest that by 2 7 ga the atmosphere and oceans had become more oxidizing substantially younger samples from the transvaal supergroup to ca 2 2 ga surprisingly have mainly low mo concentrations around 1 ppm and show no significant mo isotope fractionation relative to the continental source among possible explanations for this are a return to reducing atmospheric conditions after 2 7 ga reservoir effects or mo removal by sulfide precipitation following sulfate reduction in early proterozoic oceans

disequilibrium induced initial os isotopic heterogeneity in gram aliquots of single basaltic rock powders implications for dating and source tracing abstract the re os isotopic heterogeneity of mantle derived rocks has been well documented however it is unclear whether and how the os isotopic heterogeneity of a mantle source can influence re os isotopic dating and source tracing of mantle derived melts here we report that replicate analyses of gram aliquots of single basaltic powders one of reference material bhvo 2 and three of the hatu basalts from the western junggar region china show large variations in both os concentrations and isotopic ratios more importantly these replicate data define good apparent re os isochron correlations yielding ages significantly older than their formation ages and display remarkable correlations between the 187 os 188 os ratio and the reciprocal of the common os concentration i e 1 192 os this indicates that the initial os isotopic composition in a basaltic magmatic system may be heterogeneous and cannot be homogenized by pulverizing theoretical and mathematical deduction demonstrates that the observed apparent re os isochron correlations are the result of binary mixing without complete isotopic equilibrium at the time of formation primarily due to limited diffusional exchange of os isotopes between refractory os bearing inclusions and host minerals under mantle conditions the regressed initial os isotopic composition may bias the true value of the mantle source pulsed mantle melting and magma mixing during ascent are potential processes responsible for such initial os isotopic heterogeneity in basaltic rock systems thus when using the re os isotopic system to date and to trace the source of basaltic rocks or other rocks with relatively low os concentrations it is necessary to consider whether the initial os isotopic composition was heterogeneous or whether it had reached complete isotopic equilibrium

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

osmium in marine sediments osmium is enriched in ferromanganese minerals and its concentrations follow those of other pt group metals except pd oxidative capture during solid formation is the probable mechanism for uptake in some sediments forming under reducing conditions phosphorites and anoxic coastal deposits there is also an enrichment this may relate to reductive capture although deposits also formed under reducing conditions from hydrothermal areas are depleted in osmium

assessment of the 187re decay constant by cross calibration of re os molybdenite and u pb zircon chronometers in magmatic ore systems the past decade has seen renewed interest in 187re 187os geochronology using a variety of matrices including sulfide minerals shales and meteorites the most widely used value of the 187re decay constant 187re is 1 666 0 005 10 11 a 1 0 31 which is based on cross calibration of re os and pb pb chronometers for certain meteorites smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 however other recent studies have yielded alternate values of 187re based upon either direct counting experiments or analysis of meteorites here we provide an independent assessment of 187re using methodology sample materials and preparation of os standard solutions different from those of smoliar et al 1996 combining re os age data for molybdenite formed in magmatic ore deposits with the u pb zircon age of the magmatic rocks a refined 187re value is determined by averaging 11 individual cross calibration experiments spanning ca 2700 ma of earth history using the u decay constants of jaffey jaffey a h flynn k f glendenin l e bentley w c and essling a m 1971 precision measurement of half lives and specific activities of 235u and 238u phys rev 4 1889 1906 a value for 187re of 1 6668 0 0034 10 11 a 1 is determined using the 238u value of jaffey et al 1971 and 235u value of schoene schoene b crowley j l condon d j schmitz m d and bowring s a 2006 reassessing the uranium decay constants for geochronology using id tims u pb data geochim cosmochim acta 70 426 445 a value for 187re of 1 6689 0 0031 10 11 a 1 is determined these values are nominally higher ca 0 1 and ca 0 2 than the value determined by smoliar et al smoliar m i walker r j and morgan j w 1996 re os isotope constraints on the age of group iia iiia iva and ivb iron meteorites science 271 1099 1102 but within calculated uncertainty further refinement of 187re by cross calibrating the molybdenite and u pb zircon chronometers should be possible by utilizing high precision single grain chemical abrasion zircon u pb analyses

impact of mass movements on geo and biodiversity in the polish outer flysch carpathians complex research was simultaneously done on the geological geomorphological and biocenotic features of landslide areas in the polish outer flysch carpathians the research allowed us to define the relations between the diversity of the landslide originating landforms and the biotopes occurring within them high geodiversity diversity of landforms soil and water of landslide areas allows for a mosaic network of extremely diversified natural habitats all of these natural habitats together are characterized by a specific biodiversity dependence between geo and biodiversity in landslide areas is connected with a specific co evolution which is related to the adaptation of the ecosystems to landforms comprehensive research of this relation to landslide areas would promote the necessity to protect the landslide areas unfortunately such research done in the carpathians is still sporadic the comprehensively documented landslide areas are especially valuable elements of the nature protection network within the carpathian euro region if made reasonably accessible they may be used for didactic purposes and in geotourism

understanding volcanic geomorphology from derivatives and wavelet analysis a case study at miyakejima volcano izu islands japan abstract from feature recognition to multiscale analysis the human brain does this computation almost instantaneously but reproducing this process for effective computation is still a challenge although it is a growing field in computational geomorphology there has been only limited investigation of those issues on volcanoes for the present study we investigated miyakejima a volcanic island in the izu archipelago located 200 km south of tokyo city japan the island has experienced numerous quaternary and historical eruptions which have been recorded in details and therefore provide a solid foundation to experiment remote sensing methods and compare the results to existing data in the present study the author examines the use of dem derivatives and wavelet decomposition 5 m dem available from the geographic authority of japan was used it was pre processed to generate grid data with qgis the data was then analyzed with remote sensing techniques and wavelet analysis in envi and matlab results have shown that the combination of elevation with local data range variation and relief mapping as a rgb image composite provides a powerful visual interpretation tool but the feature separation remains a subjective analysis provided a more appropriate dataset for computer based analysis and information extraction and understanding of topographic features at different scales in order to confirm the usefulness of these topographic derivatives the results were compared to known geological features and it was found to be in accordance with the data provided by geological topographic maps and field research at miyakejima the protocol presented in the discussion can therefore be re used at other volcanoes worldwide where less information is available on past eruption and geology in order to explain the volcanic geomorphology

evaluation of current statistical approaches for predictive geomorphological mapping abstract predictive models are increasingly used in geomorphology but systematic evaluations of novel statistical techniques are still limited the aim of this study was to compare the accuracy of generalized linear models glm generalized additive models gam classification tree analysis cta neural networks ann and multiple adaptive regression splines mars in predictive geomorphological modelling five different distribution models both for non sorted and sorted patterned ground were constructed on the basis of four terrain parameters and four soil variables to evaluate the models the original data set of 9997 squares of 1 ha in size was randomly divided into model training 70 n 6998 and model evaluation sets 30 n 2999 in general active sorted patterned ground is clearly defined in upper fell areas with high slope angle and till soils active non sorted patterned ground is more common in valleys with higher soil moisture and fine scale concave topography the predictive performance of each model was evaluated using the area under the receiver operating characteristic curve auc and the kappa value the relatively high discrimination capacity of all models auc 0 85 0 88 and kappa 0 49 0 56 implies that the model s predictions provide an acceptable index of sorted and non sorted patterned ground occurrence the best performance for model calibration data for both data sets was achieved by the cta however when the predictive mapping ability was explored through the evaluation data set the model accuracies of cta decreased clearly compared to the other modelling techniques for model evaluation data mars performed marginally best our results show that the digital elevation model and soil data can be used to predict relatively robustly the activity of patterned ground in fine scale in a subarctic landscape this indicates that predictive geomorphological modelling has the advantage of providing relevant and useful information on earth surface processes over extensive areas such data being unavailable through more conventional survey methods

sources of osmium isotopes in manganese nodules abstract we have measured the 187 os 186 os and os concentrations of ferromanganese crusts forming on serpentinized peridotites from the atlantic ocean and also report major element data for these samples and six manganese nodules previously analyzed for os variations in the 187 os 186 os ratios of manganese nodules are the result of two processes operating on different spatial scales the large scale variations result from the impression of intense local os inputs from continental and oceanic sources on a generally homogeneous oceanic 187 os 186 os ratio fine scale variations may be understood as the result of the mixing of a constant fine grained debris flux of meteoritic os imposed on varying amounts of os precipitated from seawater

pge distribution in massive sulfides from the pacmanus hydrothermal field eastern manus basin papua new guinea implications for pge enrichment in some ancient volcanogenic massive sulfide deposits the distribution of platinum group elements pge in cu and zn rich samples from the roman ruins and satanic mills vent sites in the pacmanus hydrothermal field papua new guinea was studied and compared to that from selected ancient volcanogenic massive sulfide vms deposits samples from the satanic mills site are enriched in pd and rh when compared to samples from roman ruins and reach highest values in active and inactive cu rich black smoker chimneys and chalcopyrite cemented dacite breccias up to 356 ppb pd and up to 145 ppb rh a significant positive correlation was established between cu and pd and rh in samples from both vent sites comparisons of chondrite normalized patterns and values of pd pt and pd ir ratios in cu rich sulfides and probable source rocks felsic volcanic rocks morb along with the evidence for a magmatic component in the pacmanus hydrothermal system indicate that leaching of back arc volcanic rocks together with addition of magmatic volatiles to the convecting hydrothermal system was the most important factor for pge enrichment at pacmanus and likely at some pge enriched ancient vms deposits

behavior of re and os during low temperature alteration results from himalayan soils and altered black shales re os analyses were performed on five soil profiles developed on silicate lithologies in the narayani drainage basin of the himalayas as well as on several altered black shales and associated alteration phases the results indicate that all of these samples have lost large amounts of re this re loss approached 100 in the black shale derived soils which also most probably lost substantial quantities of os the near constancy of os and re concentrations with depth indicates that this loss occurred quite early in the alteration process rather than progressively during the course of soil development a slight decrease in 187os 188os was observed toward the surface of the two black shale soil profiles possibly indicating a minor preferential mobility of radiogenic 187os for this lithology in the black shale derived saprolite and soils the loss of re and os was related to the loss of organic carbon the importance of this phase is underscored by the fact that organic material separated from a black shale sample accounted for nearly all of the os contained in the whole rock analysis of alteration phases from the surface of a weathered black shale showed that os liberated during alteration was partially reprecipitated in fe oxides with os isotopic compositions very similar to that of the original rock whereas re was removed with the fluid phase these results demonstrate the disproportionately large role that black shale weathering may play in determining the re and os contents of continental runoff and thus ultimately of seawater but they also emphasize the possible complexity of this process the data suggest that a large fraction of the os contained in black shales is released during chemical alteration which is apparently not the case for most other silicate rocks therefore the potential contribution of black shales to the dissolved os budget of runoff and river water may be even greater than that expected from the high os concentrations of these rocks the extent to which this os will affect the seawater os composition depends on how efficiently it is recaptured by secondary phases such as fe mn oxides in situ or during transport these results also underscore the high mobility of re with respect to os at every stage in the erosional process thus explaining the order of magnitude increase in re os ratio from the black shale source rocks to seawater

osmium behavior in estuaries the lena river example the behavior of dissolved osmium at the river ocean interface was studied in the lena river estuary dissolved osmium removal is observed at very low salinities the loss is estimated to be 28 of the dissolved concentration of the river the removal cannot be related to the flocculation of iron oxide organic matter colloids but occurs simultaneously with the loss of aluminum the proposed mechanism is the adsorption of dissolved osmium on suspended particles in the maximum turbidity zone if this is correct then the removal of osmium in estuaries is probably a common phenomenon no contribution of osmium from the sediments is detected but neither the samples nor the stratified nature of the estuary are favorable to the study of a flux from sediments if this finding can be generalized the estimated global riverine flux of osmium to the ocean has to be recalculated and the osmium residence time in the ocean would change from 3 3 104 yr to 4 6 104 yr

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

radiometric dating of marine influenced coal using re os geochronology abstract coal deposits are integral to understanding the structural evolution and thermal history of sedimentary basins and correlating contemporeous estuarine and fluvial delatic strata with marine sections while marine shales may readily lend themselves to re os dating due to the dominance of hydrogenous re and os the lack of a chronometer for near shore sedimentary environments hampers basinwide correlations in absolute time here we employ the re os geochronometer along with total organic carbon toc and rock eval data to determine the timing and conditions of a marine incursion at the top of the matewan coal bed kanawha formation pottsville group west virginia usa the observed range for hydrogen index hi 267 290 mg hydrocarbon gram total organic carbon for these coal samples suggests dominance of aliphatic hydrocarbons with low carbon 107 6 16 4 ng g and os 0 52 0 09 ng g concentrations of the marine influenced matewan coal are higher by few orders of magnitude than published data for terrestrial coal a re os isochron for the matewan coal provides an age of 325 14 ma model 3 mswd 12 n 19 2 this is the first re os age derived from coal samples the age overlaps a new composite re os age of 317 2 ma for the immediately overlying betsie shale member external precision for replicate os analyses carried out for several matewan coal samples shows a positive correlation with their hi the hi which is low in terrestrial organic matter reflects the degree of marine influence thus samples with the most profound marine influence also have the best analytical reproducibility equilibration of os isotopes with seawater under marine conditions overwhelms variability inherited from terrestrial plant debris decreasing scatter on the isochron the 187re 188os ratios of the matewan coal 3300 5135 are higher than most of those previously published for phanerozoic black shale mostly

why terrestrial coals cannot be dated using the re os geochronometer evidence from the finnmark platform southern barents sea and the fire clay coal horizon central appalachian basin abstract coal horizons in terrestrial sedimentary sections are key to understanding the structural and thermal evolution of sedimentary basins precise and accurate age information for coal horizons can define correlations and the temporal evolution of sedimentary successions while the biostratigraphy for coal horizons yields relative ages tied to radiometric ages through the continuously refined geological time scale direct radiometric ages of coal horizons have been derived only from tonsteins lithified ash beds the re os geochronometer has been proven to record accurate and precise depositional ages for sedimentary rocks rich in organic matter however the reliability of the re os geochronometer has not yet been assessed for coals deposited in strictly terrestrial environments here in order to test the re os geochronometer we measure the re os concentrations and isotopic composition of terrestrial coals from two distinct environments the finnmark platform southern barents sea and the central appalachian basin cab samples from the finnmark platform soldogg formation also include an adjacent organic rich shale horizon the shale and two coal horizons were also analysed for total organic carbon toc and rock eval data results show that the soldogg coals and shale reached the oil generation widow tmax 448 2 c with type iii or mixed type ii iii organic matter supporting the model for deposition in overbank deposits in a fluvial setting in contrast the fire clay coals in the cab were deposited in a broad expanse of mires average re 0 5 0 4 ng g and os 23 26 pg g concentrations of terrestrial soldogg and fire clay coals are similar to those of terrestrial maghara coal and a few orders of magnitude lower than the marine influenced matewan coal elevated re os ratio os common os os corrected for ingrowth of 187os since deposition of the sample for the fire clay coals suggests highly reducing and or euxinic conditions prevailing in the water column of the extensive carboniferous peat forming mire in which these coals were deposited in contrast lower re os for soldogg coals highlight less reducing conditions likely in a short lived mire in a dynamic braided stream system re and os concentrations of terrestrial coals are on the order of re and os of plant materials and river sediments suggesting that debris from plant materials and weathered continental crust are significant contributors of re and os to terrestrial coals with some contribution from water column of the coal mire this study is the first attempt to apply the re os geochronometer on terrestrial coals in case of the soldogg coals and shale the 187re 188os vs 187os 188os relationship displays scatter with no discernible linear trend the scatter is ascribed to heterogeneity in the initial 187os 188os ratios osi and lack of post depositional isotopic equilibration during subsequent diagenesis for the fire clay coals 187os 188os and 187re 188os are well correlated linear regression of the data however does not yield a geologically reasonable age rather the linear relationship results from binary mixing between two end members the fire clay coal and tonstein suggesting that re os systematics of terrestrial coals depositing very close to tonstein beds can be significantly disturbed we conclude that the post depositional equilibration with a large re os reservoir as with a marine incursion is necessary to record a meaningful re os radiometric age for the coals

preservation of re os isotope signatures in pyrite throughout low t high p eclogite facies metamorphism pyrite in lt hp eclogites from the western tianshan orogenic belt yields a re os age of 378 1 8 9 ma which is 30 70 ma older than ages previously obtained for the same rocks using the rb sr sm nd ar ar u pb and lu hf isotope systems the tianshan lt hp eclogite experienced temperatures of up to 570 c combined with pressures of up to 2 1 gpa during metamorphism these conditions are below the transition of pyrite to pyrrhotite which defines both pyrite stability and possibly its closure temperature for re os pyrite can preserve re os signatures through eclogite facies peak metamorphic conditions and thus allow determination of the formation age of pyrite in the protolith

raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a precambrian glacial sediment extractable biomarkers can help elucidate the environment and biota of ancient glaciations although the method must be applied with care as glacial sediments have a potential for incorporation of older detrital carbon in phanerozoic glacial sediments the distinct elemental molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter however as the proterozoic biosphere was largely microbial and marine biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter here we report the combined application of raman spectroscopy and biomarker analysis to precambrian glacial sediments which together allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening precambrian sediments for immature organic matter amenable to biomarker analysis

seabed geodiversity in a glaciated shelf area the baltic sea abstract geodiversity describes the heterogeneity of the physical terrain we have performed basin wide geodiversity analysis on a glaciated epicontinental seabed to assess geodiversity measures and patterns locate areas with high geodiversity and draw conclusions on contributing processes geodiversity quantification is a rather new topic and is mainly practiced in land areas we applied geodiversity methods developed for terrestrial studies to a seabed environment three geodiversity parameters including the richness patchiness and geodiversity index of the baltic sea were assessed in a gis environment based on broad scale datasets on seabed substrates structures and bedrock a set of environmental and geological variables which were considered to reflect geological processes under seabed conditions were compared with the geodiversity to identify some of its drivers we observed differences in the geodiversity levels of the baltic subbasins which are mainly due to basement type bedrock roughness shore density and glacier derived processes the geodiversity of the baltic sea generally increases from south to north and from open sea to high shore density areas archipelagos crystalline bedrock areas provide more diverse seabed environments than sedimentary rock areas the analysis helps to inform scientists marine spatial planners and managers about abiotic conservation values the dynamics of the seabed environment and potential areas with elevated biodiversity

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

rhenium osmium isotope and platinum group element systematics of marine vs non marine organic rich sediments and coals from egypt abstract sediments rich in organic matter are important archives of paleo environmental conditions these archives are often assumed to reflect fully marine conditions however the land proximal environments where many of these archives were deposited require an understanding of the sources of matter here we investigate organic rich sediments from egypt deposited in fully marine land proximal and coastal plain environments we focus on platinum group element inventories and re os isotope systematics and combine them with organic carbon and nitrogen analyses as well as organic petrography to distinguish between terrestrial and marine sources of organic matter we show that fully marine organic rich sediments have more strongly fractionated platinum group element patterns than average continental crust that mimic that of seawater with low ir and high os pt pd and re concentrations as well as high 187 re 188 os values rhenium and os concentrations correlate well with organic carbon and nitrogen in marine organic rich sediments in contrast platinum group element concentrations in terrestrial organic rich sediments coal and land proximal shales are similar to the upper continental crust such deposits generally do not show correlations of re and os with organic carbon and nitrogen concentrations complementing re os isotope analyses with pge analyses analogous to coupled nd isotope and ree analyses aids in the interpretation of re os isochron ages and os isotope initial ratios this is particularly helpful in interpreting geochemical data from sediments deposited in environments that may have been even temporarily isolated from the open ocean and thus record local rather than global geochemical signatures

human impacts quantification on the coastal landforms of gran canaria island canary islands abstract the coastal areas of the canary islands are particularly sensitive to changes both from a natural perspective and for their potential socio economic implications in this paper the state of conservation of an insular coast is approached from a geomorphological point of view considering recent changes induced by urban and tourism development the analysis is applied to the coast of gran canaria a small atlantic island of volcanic origin subject to a high degree of human pressure on its coastal areas especially in recent decades currently much of the economic activity of gran canaria is linked to mass tourism associated with climatic and geomorphological features of the coast this work is addressed through detailed mapping of coastal landforms across the island 256 km perimeter corresponding to the period before the urban and tourism development late 19th century for the island s capital mid 20th century for the rest of the island and today the comparison between the coastal geomorphology before and after the urban and tourism development was established through four categories of human impacts related to their conservation state unaltered altered semi destroyed and extinct the results indicate that 43 of coastal landforms have been affected by human impacts while 57 remain unaltered the most affected are sedimentary landforms namely coastal dunes palaeo dunes beaches and wetlands geodiversity loss was also evaluated by applying two diversity indices the coastal geodiversity loss by total or partial destruction of landforms is estimated at 15 2 according to shannon index h while it increases to 32 1 according to an index proposed in this paper we conclude that the transformations of the coast of gran canaria induced by urban and tourism development have heavily affected the most singular coastal landforms dunes palaeo dunes and wetlands reducing significantly its geodiversity

the importance of organic rich shales to the geochemical cycles of rhenium and osmium abstract the role that marine organic rich sediments play in the surficial osmium and rhenium cycles has been assumed to be important due to the high re os ratios and high concentrations of these elements in such reducing sediments compared to the average continental crust the high re os leads to rapidly increasing 187os 188os ratios we determine how large a role these sediments play in the surficial osmium and rhenium budgets by compiling a geochemical database to quantify the mean 187re 188os and 187os 188os ratios of organic rich sediments we then utilize estimates of the abundance of organic rich sediments in the geologic record of different ages to estimate an average 187os 188os for these sediments we find that the calculated 187os 188os value of organic rich sediments varies between 2 22 and 2 27 depending on the volume age model used with error estimates of 2 07 to 2 42 and 2 12 to 2 48 respectively despite the fact that these sediments constitute a relatively small proportion of the upper continental crust they contribute a disproportionately large amount 50 to the upper continental crustal rhenium and to a lesser extent 5 10 osmium inventories owing to their high concentrations of these elements

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

a complete os excursion across a terrestrial cretaceous paleogene boundary at the west bijou site colorado with evidence for recent open system behavior abstract the few previously reported values of 187os 188os ratios from non marine k pg boundary sections are distinctly higher than the range of 187os 188os ratios measured in chondrites and the range of ratios predicted by models of physical mixing between chondrites and upper crust here re os data from the west bijou continental k pg boundary site located within the denver basin are used to better constrain the os isotopic composition of fallout from the chicxulub ejecta plume for the first time full vertical profiles of 187os 188os ratios and re and os concentrations across a continental k pg boundary section are reported within this section of lignite the lowest measured 187os 188os ratio 0 182 coincides with the k pg boundary interval as previously determined by palynology and the distribution of shocked quartz in a nearby outcrop however sediments with elevated os concentrations and measured 187os 188os below 0 23 extend over a 30 cm interval from 5 cm above the clay rich boundary interval 5 cm thick to 25 cm below maximum ir and os concentrations occur 3 cm and 10 cm below the k pg boundary respectively demonstrating greater diagenetic mobility of os relative to ir low 187os 188os above the k pg boundary suggests that accumulation of impact derived os at this site persisted after the impact event perhaps due to redistribution of impact debris in the surrounding area importantly calculated initial 187os 188os ratios throughout most of the section are impossibly low and require open system behavior likely in the form of re addition within the last 10 million years within the boundary interval re concentrations are among the lowest measured at bowring pit and calculated initial 187os 188os ratios are very similar to those previously reported from the western interior of the united states k pg boundary material 0 14 suggesting super chondritic 187os 188os is characteristic of the chicxulub ejecta plume beyond implications for our understanding of os as an impact tracer this study emphasizes the dramatic effect diagenesis can have on the re os system in organic rich environments especially through post depositional addition of re

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass