the ktb apatite fission track profiles building on a firm foundation abstract deep boreholes serve as natural laboratories for testing thermochronometers under geological conditions the kontinentale tiefbohrung ktb is an interesting candidate because the geological evidence suggests that approximate isothermal holding since the last documented exhumation in the late cretaceous to palaeocene is a reasonable assumption for the thermal histories of the ktb samples we report 30 new apatite fission track ages and 50 new mean confined track lengths determined on cores from the 4 km deep pilot hole the and external detector ages are consistent with the population ages from earlier studies and together define a clear age profile the mean track lengths from this and earlier studies reveal the effects of experimental factors the measured age and length profiles are compared with the predictions of 24 annealing models for isothermal holding there are clear discrepancies between the measured and calculated profiles down to 1 5 km depth the measured mean track lengths are shorter than the predicted the balance of methodological evidence indicates that this is due to seasoning i e a shortening of the fossil confined tracks without attendant age reduction from 2 5 to 4 0 km depth the mean track lengths are longer than the predictions this suggests that the bias model that weights the probabilities of observing tracks of different length and which is based on experiments relating surface track densities to mean track lengths is not appropriate for confined tracks experimental and methodological factors are sometimes difficult to disentangle but present a sufficient margin for there to be no need to go against the independent geological evidence unknown geological events cannot be ruled out but their existence cannot be inferred from the fission track data alone much less can the nature or magnitude of such events be specified

mineralogy geochemistry and fluid action process of uranium deposits in the zhiluo formation ordos basin china abstract some controversies still exist regarding the genesis of sandstone type uranium deposits in the northeastern ordos basin herein based on boreholes and well logging data we selected sandstone samples representing different epigenetic alteration environments as the research object and comprehensively utilized polarizing microscopy scanning electron microscopy electron probe analysis elemental analysis and other test methods to research sandstone genesis the main altered minerals in the sandstone of this area include limonite pyrite achavalite carbonate sulfate clay and uranium minerals the complex characteristics of alteration minerals indicate multi stage fluid mixed mineralization in this area according to the relationship between the major elements in different types of sand bodies the components were classified into three groups the first is the reduction media group including cao mno total oxygen carbon toc s u and burning loss the second is the detrital particle group including sio2 k2o and na2o and the third contains the clay and volcano component group including fe2o3 p2o5 tio2 feo mgo and al2o3 among these the content of reduction media is positively correlated with uranium enrichment whereas detrital particles and clay components reflect the influence of alteration on the sand body composition which indirectly affects the uranium adsorption and precipitation through the normalization of rare earth element ree chondrites we find that the distribution patterns of rees in rocks with different geochemical environments show a fractionation of light and heavy rare earth elements hrees a right leaning enrichment of light rare earth elements lrees and relatively flat hree further via the post archean australian shale paas normalization we observe that the mudstone of the zhiluo formation exhibits a relatively flat curve whereas the sandstones have strongly positive eu anomalies the difference in ree values for different types of sand bodies indicates that although all types of rocks have a similar sedimentary environment their original sediments underwent fluid alterations such as oxidation and reduction based on the uranium mineralization evolution history in the study area the water rock reaction process and mineral alteration sequence were determined on the basis of alteration types and elemental concentrations our findings provide new insight into the petrological significance mineralogy and geochemical composition of uranium deposits in the ordos basin

linking soil element mass transfer to microscale mineral weathering across a semiarid environmental gradient abstract understanding controls on silicate weathering is critical to characterizing critical zone evolution the objective of this study was to investigate how climate vegetation and landscape position control feldspar transformations across a semiarid environmental gradient granitic surface soil and saprock samples were collected from desert scrub and mixed conifer sites within the santa catalina mountain critical zone observatory where mean annual temperature ranges from 24 c to 10 c and mean annual precipitation from 25 to 85 cm quantitative x ray diffraction x ray fluorescence and electron microprobe analyses were employed to quantify elemental changes in bulk soils and across plagioclase grains the chemical depletion of na in bulk soils ranged from 5 4 15 in the desert scrub sites relative to 16 33 in the mixed conifer sites plagioclase grain alteration was classified into unaltered edge and altered sections to compare microscale weathering and elemental variation the na al and si al ratios decreased from unaltered to edge to altered grain sections in the mixed conifer sites whereas the element ratios of the desert scrub system were similar between unaltered and edge grain sections and only exhibited significant decreases in na al and si al ratios between edge and altered materials the microscale depletion of na and si suggested increased silicate weathering in the cooler wetter and more biologically productive mixed conifer system compared to the hot dry desert scrub system the results also demonstrated a topographic control on mineral transformation where increased plagioclase weathering occurred in convergent footslope landscapes with little change in elemental depletion of soils in divergent summit sites

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

predicting the state of the southern oscillation using principal oscillation pattern analysis abstract principal oscillation pattern pop analysis is a diagnostic technique for deriving the space time characteristics of a dataset objectively a multiyear dataset of monthly mean sea level pressure slp in the area 15 s to 40 s is examined with the pop technique in the low frequency band one physically significant pair of patterns is identified which is clearly associated with the southern oscillation so according to the pop analysis the 50 may be described as a damped oscillatory sequence of patterns p1 p2 p1 p2 p1 having a time scale of two to three years the first pattern p1 representative of the peak phase of enso exhibits a dipole with anomalies of opposite sign over the central and eastern pacific and over the indian ocean australian sector the second p2 pattern is dominated by an anomaly in the spcz region and describes an intermediate or onset phase the time coefficients of the two patterns p1 and p2 may be interpreted as a bivariate index of the so generalizing

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

the brahmaputra tale of tectonics and erosion early miocene river capture in the eastern himalaya the himalayan orogen provides a type example on which a number of models of the causes and consequences of crustal deformation are based and it has been suggested that it is the site of a variety of feedbacks between tectonics and erosion within the broader orogen fluvial drainages partly reflect surface uplift different climatic zones and a response to crustal deformation in the eastern himalaya the unusual drainage configuration of the yarlung tsangpo brahmaputra river has been interpreted either as antecedent drainage distorted by the india asia collision and as such applied as a passive strain marker of lateral extrusion latest neogene tectonically induced river capture or glacial damming induced river diversion events here we apply a multi technique approach to the neogene paleo brahmaputra deposits of the surma basin bengal basin bangladesh to test the long debated occurrence and timing of river capture of the yarlung tsangpo by the brahmaputra river we provide u pb detrital zircon and rutile isotopic sr nd and hf and petrographic evidence consistent with river capture of the yarlung tsangpo by the brahmaputra river in the early miocene we document influx of cretaceous paleogene zircons in early miocene sediments of the paleo brahmaputra river that we interpret as first influx of material from the asian plate transhimalayan arc indicative of yarlung tsangpo contribution prior to capture the predominantly precambrian paleozoic zircons indicate that only the indian plate was drained contemporaneous with transhimalayan influx reflecting the river capture we record arrival of detrital material affected by cenozoic metamorphism as indicated by rutiles and zircons with cenozoic u pb ages and an increase in metamorphic grade of detritus as recorded by petrography we interpret this as due to a progressively increasing contribution from the erosion of the metamorphosed core of the orogen whole rock sr nd isotopic data from the same samples provide further support to this interpretation river capture may have been caused by a change in relative base level due to uplift of the tibetan plateau assuming such river capture occurred via the siang river in the early miocene we refute the tectonic aneurysm model of tectonic erosion coupling between river capture and rapid exhumation of the eastern syntaxis since a time interval of at least 10 ma between these two events is now demonstrated this work is also the first to highlight u pb dating on detrital rutile as a powerful approach in provenance studies in the himalaya in combination with zircon u pb chronology

impact of rainfall and topography on the distribution of clays and major cations in granitic catenas of southern africa abstract soil catenas integrate and amplify gravity transfer and differentiation processes of eluviation and illuviation in soil profiles we quantified differences in these redistribution processes along granitic catenas across an arid to sub humid climate gradient in kruger national park south africa we measured soil properties in nine catenas sampled from three areas receiving annual rainfall of 470 mm arid zone 550 mm semi arid zone and 730 mm sub humid zone as rainfall increased kaolinite replaced smectite as the dominant clay mineral in all landscape positions across the catenas toeslopes showed the strongest evidence of this transition with an excess of smectite in the arid catenas but complete prevalence of kaolinite in toeslopes of sub humid catenas the concentration and distribution of clay along the catenas were dependent on landscape position as well soil profiles at and near the crests were clay depleted as low as 1 while those at the toeslopes had much more clay up to 60 clay redistribution along catenas was sensitive to climate with the least amount of redistribution occurring in the dry sites and the most occurring in the wet sites as a consequence the sub humid catenas had clay accumulation only in a small part of the toeslopes while the bulk of their length was represented by highly leached soils in contrast arid zone catenas showed little clay redistribution and semi arid sites displayed the greatest within catena clay redistribution and preservation clay movement and storage conditioned other soil properties such as cec base cation distribution base saturation and ph

basin related uranium mineral systems in australia a review of critical features abstract this paper reviews critical features of basin related uranium mineral systems in australia these mineral systems include proterozoic unconformity related uranium systems formed predominantly from diagenetic fluids expelled from sandstones overlying the unconformity sandstone hosted uranium systems formed from the influx of oxidised groundwaters through sandstone aquifers and calcrete uranium systems formed from oxidised groundwaters flowing through palaeochannel aquifers sand and calcrete the review uses the so called source pathway trap paradigm to summarise critical features of fertile mineral systems however the scheme is expanded to include information on the geological setting age and relative timing of mineralisation and preservation of mineral systems the critical features are also summarised in three separate tables these features can provide the basis to conduct mineral potential and prospectivity analysis in an area such analysis requires identification of mappable signatures of above mentioned critical features in geological geophysical and geochemical datasets the review of fertile basin related systems shows that these systems require the presence of at least four ingredients a source of leachable uranium and vanadium and potassium for calcrete uranium deposits suitable hydrological architecture enabling connection between the source and the sink site of accumulation physical and chemical sinks or traps and a post mineralisation setting favourable for preservation the review also discusses factors that may control the efficiency of mineral systems assuming that world class deposits result from more efficient mineral systems the review presents a brief discussion of factors which may have controlled the formation of large deposits in the lake frome region in south australia the chu sarysu and syrdarya basins in kazakhstan and calcrete uranium deposits in the yilgarn region western australia

along strike segmentation of the abanico basin central chile new chronological geochemical and structural constraints the andes of central chile are composed mostly of cenozoic volcanic rocks erupted during the opening and subsequent inversion of the intra arc volcano tectonic abanico basin until recently the internal segmentation of this inverted basin was poorly understood based on a combination of u pb geochronology u th he thermochronology whole rock geochemistry and structural data we propose that the abanico basin can be divided into two main segments separated by the nw striking piuquencillo fault and conjugate ne striking faults stratigraphic units defined in the northern segment abanico and farellones formations cannot be correlated with the rocks of the southern segment coya machali formation and teniente volcanic complex in terms of lithofacies depositional ages and geochemistry the northern and southern segments also show temporal differences in their tectonic evolution an early deformation event beginning at 22 ma affected only the northern segment and is associated with the formation of progressive unconformities between the abanico and farellones formations and also with crustal thickening as reflected in the geochemistry of the farellones formation a second stage of crustal thickening and exhumation began at 12 ma as suggested by a sharp increase of the la yb ratios in the northern segment in the southern segment this event is reflected by only a moderate increase of la yb ratios and by the transition between the coya machali formation and the teniente volcanic complex finally a third stage of exhumation and crustal thickening beginning at 7 ma affected both the northern and southern segments this last stage was the main exhumation event affecting the rocks of the andes of central chile and is recorded in the geochemistry of igneous rocks by a sharp increase in the la yb ratios in the southern segment

miocene rise of the shillong plateau and the beginning of the end for the eastern himalaya abstract a common feature of convergent plate boundaries is the self organization of strain exhumation and topography along discrete arcuate boundaries deviations from this geometry can represent first order changes in stress applied at a plate boundary that must affect how strain is partitioned within the interior of an orogen the simplicity of the himalayan fold and thrust belt seen along its central portion breaks down along the eastern extremity of the arc where the 400 km long shillong plateau has developed this change in strain partitioning affects nearly 25 of the arc and has not previously been considered to be important to the orogen s development new low temperature thermochronometry data suggest this structure initiated in mid to late miocene time significantly earlier than was previously estimated from the sedimentary record alone development of the shillong plateau may be linked to a number of kinematic changes within the himalayan and burman collision zones that occur at the same time these events include the onset of e w extension in central tibet eastward expansion of high topography of the tibetan plateau onset of rotation of crustal fragments in southeastern tibet and re establishment of eastward subduction beneath the indo burman ranges we suggest that the coincidence of these tectonic events is related to the dismemberment of the eastern himalayan arc signifying a change in regional stress applied along the india eurasia burma plate boundaries discrepancies between vertical long term faulting rates and geodetically derived far field convergence rates suggest that the collisional boundary in the eastern himalayan system may be poorly coupled due to introduction of oceanic and transitional crust into the eastern plate boundary the introduction of dense material into the plate boundary late in the orogen s history may explain regional changes in the strain field that affect not only the himalaya but also the deformation field more than 1000 km into the tibetan plateau

detrital apatite fission track evidence for provenance change in the subei basin and implications for the tectonic uplift of the danghe nan shan nw china since the mid miocene abstract the subei basin is located at the intersection of the northeastern end of the altyn tagh fault atf and the western end of the danghe nan shan in the northeastern tibetan plateau the basin contains up to 4000 m thick cenozoic terrestrial clastic sediments which contain information on the uplift of the danghe nan shan in order to estimate the detrital apatite thermochronology with fission track dating we collected eight sandstone samples from the tiejianggou section of the subei basin which has an established depositional age range from 22 8 to 9 ma we found that a distinct change in slope of the peak age and lag time of the detrital apatite fission track occurred at 14 ma which we interpret as a provenance change caused by the uplift of the western end of the danghe nan shan combined with previous studies in adjacent areas this work implies that the initiation of successive episodes of surface uplift in the northeastern margin of the tibetan plateau took place in the mid miocene

interplay between soil formation and geomorphic processes along a soil catena in a mediterranean mountain landscape an integrated pedological and geophysical approach soil spatial distribution often shows high variability because of geo environmental settings affecting soil formation and geomorphic processes the paper describes a combined pedological geophysical approach for investigating the interplay among soil forming processes geomorphic dynamics and physico chemical soil properties in a soil catena in a mediterranean mountain landscape southern italy stocks of soil organic carbon soc and total nitrogen stn were determined and their interactions with slope position analyzed five slope units were defined along the soil catena summit shoulder back foot and toe slopes and in each of them a soil profile was dug and analyzed thickness of soil horizons and contact between soil and parent material were determined by a 2d electrical resistivity tomography survey results showed granitic bedrock is characterized by vary weathering degrees strongly affecting soil type development moreover soil properties variation is related to topographic features and water erosion processes soil chemical composition showed high values of sio2 and al2o3 probably due to inheritance from underlying granitic parent material particularly fe2o3 content increased with weathering conditions as shown by chemical index of alteration values along foot and toe slopes reworking and accumulation of colluvial soil lead to the formation of thicker accretionary a horizon consequently summit areas together with foot and toe slopes had greater soc and stn stocks than back and shoulder slopes that because soils are thicker and richer in soc on summit and valley bottom than in shoulder and back slope positions the proposed approach has showed the benefit of an integrated methodology for investigating spatial variations along soil catenas

late cretaceous cenozoic tectonic sedimentary evolution and u enrichment in the southern songliao basin abstract late cretaceous cenozoic tectonic sedimentary evolution is fundamental to u uranium migration and u enrichment in the southern songliao basin northeast china to establish the genetic connection between tectonic sedimentary evolution and u enrichment this paper presents a mineralogical study apatite fission track aft analysis and sem cl analysis of quartz grains two stages of mineralization were proposed including the u pre enrichment stage during the late cretaceous and the ore forming stage during the cenozoic based on the density plots of the aft ages paleoclimate studies and sem cl analysis of quartz grains it is inferred that the u pre enrichment was closely related to the rapid uplift of the great xing an range and the zhangguangcai range and the o2 rich atmosphere during 97 90 ma in the southern songliao basin the o2 rich atmosphere increased u mobility and led to the formation of red beds during the late cretaceous which widely developed u pre enrichment in the basins of northeast china the mineralogical study reveals that the qianjiadian uranium deposit developed in two stages the diagenetic process experienced the transition from early alkaline to late acidic conditions to promote the stage i mineralization u pre enrichment the dominant occurrence spaces for u were the dissolution pores of quartz tightly packed with calcite cement u enrichment during alkaline ambient conditions was mainly via adsorption with the increase of the buried depth the early alkaline diagenesis returned to acidic conditions due to the abundant organic material u vi was reduced to pitchblende due to the reducing capacity of the organic matter om stage ii ore forming stage mineralization was strictly related to the hydrocarbon re concentration according to the thermal history study of the cc1 and q2 boreholes the southern songliao basin experienced four episodes of rapid uplift during the cenozoic at 83 80 ma 68 52 ma 33 23 ma and 8 ma respectively the cenozoic uplifts led to hydrocarbon migration at 65 ma 23 ma and present the re concentration of hydrocarbon prompted the u mineralization in the qianjiadian uranium deposit in the southern songliao basin during the stable period of tectonic movements the reducing conditions caused by hydrocarbons promoted u mineralization the dominant spaces of coffinite were intergranular dissolved pores formed during the transformation from the feldspar to the kaolinite under acidic conditions the post rift phase and structural inversion phase directly controlled the u pre enrichment stage and the ore forming stage respectively overall the tectonic sedimentary evolution played an important role in controlling the u leaching from granites the dominant occurrence spaces and u recycling

south menderes monocline low temperature thermochronology constrains role of crustal extension in structural evolution of southwest turkey abstract we report apatite and zircon fission track data across the contact zones between the menderes nappes the cycladic blueschist unit and the oren nappe in the anatolide belt of southwest turkey these data resolve previous debate on the deformation history of these cretaceous to eocene nappe contacts including whether they were reactivated during late oligocene to miocene crustal extension apatite fission track ages range from 18 to 28 ma in the menderes nappes and 31 to 42 ma in the oren nappe zircon fission track ages are 29 to 31 ma in the menderes nappes 30 to 33 ma in the cycladic blueschist unit and between 93 ma and 129 ma in the oren nappe the data reveal that the tectonic contacts within the menderes nappes and with the overlying cycladic blueschist unit have been sealed since 35 30 ma in the oren nappe zircon fission track ages are distinctly older with mixed single grain ages between 300 and 75 ma reflecting partial to full resetting during late cretaceous high pressure metamorphism the contact between the cycladic blueschist unit and the oren nappe shows no significant tectonic movement in the brittle crust after 70 ma these data reveal that the nappe boundaries in the southern menderes massif have undergone no significant differential offset relative to the earth s surface since the oligocene and therefore were not reactivated during late oligocene to miocene continental extension we interpret the steeply dipping portion of the nappe pile in the southern menderes massif as a tilted crustal section which we name the south menderes monocline we speculate this monocline formed by differential uplift in the miocene either at the hinge zone of a plateau or by unloading of the simav detachment footwall

persistent u iv and u vi following in situ recovery isr mining of a sandstone uranium deposit wyoming usa abstract drill core samples from a sandstone hosted uranium u deposit in wyoming were characterized to determine the abundance and distribution of uranium following in situ recovery isr mining with oxygen and carbon dioxide enriched water concentrations of uranium collected from ten depth intervals ranged from 5 to 1920 ppm a composite sample contained 750 ppm uranium with an average oxidation state of 54 u vi and 46 u iv scanning electron microscopy sem indicated rare high uranium 1000 ppm u in spatial association with p ca and si o attributed to relict uranium minerals possibly coffinite uraninite and autunite trapped within low permeability layers bypassed during isr mining fission track analysis revealed lower but still elevated concentrations of u in the clay silica matrix and organic matter several 10 s ppm and yet higher concentrations associated with fe rich s poor sites likely iron oxides on altered chlorite or euhedral pyrite surfaces but not on framboidal pyrite organic c

tracing recent environmental changes and pedogenesis using geochemistry and micromorphology of alluvial soils sabie sand river basin south africa abstract three pedons on the alluvial terraces of the sabie sand river basin within kruger national park south africa were studied to improve our understanding of recent environmental changes and assess degree of chemical weathering and pedogenesis in the area using geochemical and micromorphology proxies particle size distributions were obtained using malvern mastersizer soil geochemistry was determined by xrf and thin sections by routine laboratory procedures the soils are predominantly sandy 94 sand in all samples the mean phi values of the soils had little variation suggesting that reworking of sediments upwards in individual profiles produced a more uniform pedogenesis rather than coming from different physical sources calcification is the dominant pedogenic process in these alluvial soils the chemical index of alteration cia proved a more suitable index than chemical index of weathering ciw for evaluating weathering in the terraces the micromass and b fabrics are mostly granostriated and partly brown mosaic speckled miseca values for the degree of soil development range from 4 to 9 which mean weakly to moderately developed soils coarse secondary calcite nodules and coatings are responsible for cementation as observed in pedon 2 which suggests calcium carbonate precipitation from periodical flooding and evaporating groundwater events the features and diagnostic properties of the soils on the alluvial terraces along the sabie sand river provide evidence for land surface impacts of recent environmental changes in this internationally important conservation area precise dating of calcium carbonate precipitates is however needed to put the observed evidence into a wider geochronological perspective

principal oscillation pattern analysis of the 30 to 60 day oscillation in general circulation model equatorial troposphere a new technique is described for identifying time dependent patterns i e principal oscillation patterns or pops in a set of geophysical time series pops are defined as the normal modes of a linear dynamical representation of the data in terms of a first order autoregressive vector process with residual noise forcing pops associated with real eigenvalues represent nonpropagating nonoscillatory patterns which decay exponentially pops associated with complex eigenvalues occur in complex conjugate pairs and can represent standing wave structures if one pattern is much stronger than the other propagating waves if both patterns are periodic and have the same structure except for a quarter wavelength shift or in general an arbitrary amphidromal oscillation after the pops have been defined for a selected set of primary variables associated correlation or composite patterns may be derived for additional secondary fields to gain further insight into the structure of the interaction mechanisms the method is illustrated by analyzing the tropical variability structure of a 10 year numerical simulation with the t21 general circulation model gcm of the european centre for medium range weather forecasts reading england the pop analysis is applied to the 200 hpa horizontal divergence field along the equator for time scales shorter than 10 weeks the associated patterns are determined for a number of additional fields in the tropical belt between 30 s and 30 n one dominant pop pair is found its spatial scale corresponds to zonal wave number 1 the patterns travel eastward with an average period of 24 days and an e folding decay time of 10 days the maximum variance occurs in the area with maximum tropical precipitation between 100 e and the dateline these features correspond rather closely to the characteristics of the observed tropical 30 to 60 day wave except for the smaller period a frequency wave number analysis confirms that this 30 to 60 day wave is the most dominant regular oscillation in the tropical gcm troposphere the associated patterns of sea level pressure precipitation and other quantities exhibit a number of intriguing aspects namely 1 the phase velocity of the 30 to 60 day wave varies with longitude from 6 m s 1 in the indonesian area to more than 30 m s 1 over the eastern pacific small phase speeds being associated with large amplitudes and high phase speeds with small amplitudes 2 in the high amplitude regions rainfall and upper air velocity potential are in phase while in the low amplitude regions rainfall and velocity potential appear uncorrelated 3 at the surface a pattern strongly resembling gill s theoretical response to an equatorial heating source is found with a trough to the east and two off equatorial cyclones to the west of the heating the lack of meridional winds is probably related to the disregard of the seasonal asymmetries

age of uranium mineralization at the highland mine powder river basin wyoming as indicated by u pb isotope analyses most of the uranium deposits in the powder river basin occur at various stratigraphic levels in the wasatch formation of eocene age but pollen and spores found in the highland mine host rocks indicate that the deposits here may be in the upper part of the fort union formation of paleocene age analyses of u pb isotopes in several samples of ore from the highland mine were made in order to compare the apparent age of mineralization of this deposit with that of host rocks of equivalent age at gas hills crooks gap and shirley basin wyoming the samples used for age determinations were collected in the southernmost of a series of open pit mines and in the uppermost of the three host units all samples contain only reduced uranium minerals which are mainly coprecipitated mixtures of pitchblende and coffinite sample ep17 7 consists of ore at the boundary with oxidized yellow sandstone and sample ep17 8 of ore 6 m 20 ft from the interface with oxidized sandstone sample j represents calcite cemented ore from a thin zone at the base of the upper host sandstone unit lower limb ore the others are randomly selected grab samples of mineralized material in the oremore deposit at the same level as ep 17 7 with the exception of sample j all samples were collected from exposures of ore on the pit floor 60 m 200 ft below the original land surface and at an elevation of 5 060 feet sample j came from the pit floor at an elevation of about 5 040 ft less

slab detachment beneath eastern anatolia a possible cause for the formation of the north anatolian fault in this paper we discuss the possibility that the north anatolian fault naf results from the deep deformation of the slab beneath the bitlis hellenic subduction zone we described the tectonic evolution of the anatolia aegean area in three main steps before during and after the formation of the naf we remark that the tectonic conditions that are assumed to have triggered the formation of the naf i e collision to the east and extension to the west was already achieved before the onset of that strike slip fault system we also highlight that the formation of the naf was accompanied by the uplift of the turkish iranian plateau and by a surge of volcanism in the eastern anatolia collisional area and probably by the acceleration of the aegean trench retreat we show tomographic images from global p wave model of piromallo and morelli c piromallo a morelli p wave tomography of the mantle under the alpine mediterranean area j geophys res 108 2003 doi 10 1029 2002jb001757 showing that the slab beneath the bitlis collisional belt is not continuous and that its possible rupture pursues to the west at least up to cyprus and possibly up to the eastern end of the hellenic trench all these observations suggest that the plate tectonic re organization occurred in the late miocene early pliocene in the region results from slab break off in the bitlis area and from its lateral propagation to the west this idea is tested in analogue laboratory experiments which confirm that the break of the slab under the collisional belt may trigger 1 the acceleration of slab retreat to the west due to the increase in slab pull force 2 the indentation of the continent in the collisional area and 3 produce the conditions that permit the lateral escape of material towards the west and the formation of the naf

geomorphic development of the escarpment of the eritrean margin southern red sea from combined apatite fission track and u th he thermochronometry apatite u th he and fission track thermochronometers are combined to constrain models of denudation and escarpment development of the high elevation eritrean margin along the southern red sea u th he ages have been determined for apatites from two coast perpendicular transects that were previously used for apatite fission track analysis e abbate m l balestrieri g bigazzi morphostructural development of the eritrean rift flank southern red sea inferred from apatite fission track analysis j geophys res 107 b11 doi 10 1029 2001jb001009 2002 in central eritrea near asmara he ages increase from c 7 ma at the coast to 152 ma on the plateau along a transect further south he ages from the margin border to the base of the escarpment span a narrower range 7 to 12 ma one sample from the top of a marginal high 2950 m yields older ages 22 43 ma forward modeling suggests that the he age distribution across the margin should allow scarp retreat and downwearing mechanisms to be distinguished in the case of a margin formed in the last twenty million years the distribution of he ages suggests that the escarpment evolved by downwearing and that post break up erosion of the escarpment was facilitated by in situ excavation rather than parallel retreat this implies the existence of an inland drainage divide located seaward of the present day escarpment rim we envisage that the inland divide formed during or immediately after continent break up and that the eastern marginal belt represents a remnant of the apex structure the short distance between the eastern marginal belt and the rim c 10 km represents the total retreat of the escarpment comparison of the measured he ages from the coastal plain with those predicted from forward modelling indicates that the main phase of post break up erosion started at about 15 ma closer to the initiation of seafloor spreading in the red sea than was thought previously

cenozoic tectonics of new guinea major hydrocarbon discoveries have been made in eastern and westernmost new guinea and there is great potential for additional discoveries although the island is a type locality for arc continent collision during the cenozoic the age number and plate kinematics of the events that formed the island are vigorously argued the northern part of the island is underlain by rocks with oceanic island arc affinities and the southern part is underlain by the australian continental crust based on regional sedimentation patterns it is argued herein that the cenozoic tectonic history of the island involves two distinct collisional orogenic events the first cenozoic event the peninsular orogeny of oligocene age 35 30 ma was restricted to easternmost new guinea emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the australian continent beneath part of the inner melanesian arc this collision uplifted the papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the aure trough between the oligocene and miocene the paleogeography of the region was similar to present day new caledonia the continental crust under central and western new guinea remained a passive margin the second event the central range orogeny began in the latest middle miocene when the bulldozing of australian passive margin strata first created emergent uplifts above a north dipping subduction zone beneath the western part of the outer melanesian arc the cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the australian continental basement is dated at about 12 ma this collision emplaced the irian ophiolite and created the present mountainous topography forming the spine of the island

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

the global middle and late miocene and the deep earth model for earlier orogenies abstract the 11 ma middle and late miocene interval forms only 2 of phanerozoic time but includes two broadly contemporaneous global orogenies one reaching across southern eurasia and the other spanning the circumpacific these two global orogenies caused many global events and because they are close to us in time causality links between these orogenies and these far scattered events are much more apparent than in older orogenies these teleconnections include establishment of the present world oceanic current system the beginnings of oceanic cooling at 14 ma an increase in hemipelagic mud bordering the continents changes in continental tilts and river systems great biological changes increased desertification replacement of c 3 by c 4 grasses a major shift in siliceous microfossils from the atlantic to the pacific at 15 ma and first development of the earliest hominids in east africa starting at 10 ma in addition spreading rates of oceanic ridges increased volcanism increased there was movement along many transform faults and continental elevations increased short bulleted statements set forth these near and far field events immediate causes were increased rates of plate motions and or changes of directions only a strong short 11 ma pulse of heat from the earth s core provides the logical ultimate source of this energy only such a pulse of heat from the core has sufficient magnitude and acts globally thus the deep earth cycle is a plausible easy to understand overarching explanation that should be increasingly considered by geologists and geophysicists studying the outer crust a flow diagram links major earth surface features on the continents to the deep earth alternative explanations for these events are considered and seem totally inadequate

uranium isotope composition of waters from south texas uranium ore deposits redox conditions and associated changes in mobility of uranium u are tightly linked to a multitude of challenges connected with u mining in sandstone hosted deposits and new methods that directly measure reduction or oxidation of u can inform on these questions a novel proxy for understanding u redox chemistry has recently emerged the volume dependent isotopic fractionation of uranium 238 238u from uranium 235 235u novel measurements of 238u 235u isotopic ratio are combined with measurements of the more commonly utilized uranium 234 uranium 238 activity 234u 238u ratio as both isotopic ratios can be measured simultaneously however application of both u isotopic ratios in the contexts of exploration and environmental remediation of u ores requires characterization of these isotopic ratios across a variety of redox settings here 238u 235u and 234u 238u ratios are examined from eight transects in two u ore bodies the rosita and kingsville dome deposits in south texas these sites are classic roll front deposits and exhibit a wide variety of both natural and altered redox conditions across all transects it is observed that 234u 238u ratios decrease systematically towards the ore body from both the oxidizing and reducing sides irrespective of whether the site has been mined or not this pattern reflects geologically recent and significant u leaching and mobility and is characteristic of active roll fronts overall 238u values in these transects decrease systematically towards the reducing zone a simple rayleigh fractionation model where u ore is deposited from an increasingly isotopically depleted reservoir of dissolved u best explains the overall trend very negative 238u values likely reflect multiple cycles of u deposition and dissolution the south texas data set indicates that both 234u 238u ratios and 238u values can be variable at an individual mine site however overall low 234u 238u ratios and negative 238u values are characteristic of active roll front deposits the comprehensive u isotopic composition of both ores and well waters represents a powerful new tool in prospecting of sandstone hosted u ore and in environmental remediation following extraction of u ore

apatite fission track and u th he ages from the higher himalayan crystallines kaghan valley pakistan implications for an eocene plateau and oligocene to pliocene exhumation abstract apatite fission track and apatite and zircon u th he ages were obtained from high and ultra high pressure rocks from the kaghan valley pakistan four samples from the high altitude northern parts of the valley yielded apatite fission track ages between 24 5 3 7 and 15 6 2 1 ma and apatite u th he ages between 21 0 0 6 and 5 3 0 2 ma these data record cooling of the formerly deeply subducted high grade metamorphic rocks induced by denudation and exhumation consistent with extension and back sliding along the reactivated normal acting main mantle thrust overlap at around 10 ma between fission track and u th he ages is recognised at one location besal showing that fast cooling occurred due to brittle reactivation of a former thrust fault widespread miocene cooling is also evident in adjacent areas to the west deosai plateau tso morari most likely related to uplift and unroofing linked to continued underplating of the indian lower crust beneath ladakh and kohistan in the late eocene to oligocene in the southernmost part of the study area near naran two significantly younger late miocene to pliocene apatite fission track ages of 7 6 2 1 to 4 0 0 5 ma suggest a spatial and temporal separation of exhumation processes these younger ages are best explained by enhanced late miocene uplift and erosion driven by thrusting along the main boundary thrust

post late paleozoic tectonism in the southern catalan coastal ranges ne spain assessed by apatite fission track analysis abstract we report the first apatite fission track thermochronologic data for 17 samples from the southern catalan coastal ranges of ne spain thermal histories of carboniferous metasediments late hercynian intrusions and lower triassic buntsandstein sediments from three tectonic blocks miramar prades and priorat are derived and interpreted within the geodynamic framework and tectonic evolution of the region the apatite fission track ages range from 198 24 to 38 5 ma and mean fission track lengths are all

global miocene tectonics and the modern world abstract an amazing congruence of seemingly unrelated diverse global events began in the middle and upper miocene and established our modern world two global orogenic belts were active mostly in the middle and upper miocene while backarc basins formed along the eastern margin of asia coincident with these events global temperatures cooled in both the ocean and atmosphere desertification occurred from central asia into and across most of northern africa and also in australia and in southern south america coincident with the expansion of the antarctic ice cap at 14 ma there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation muddy pelagic sedimentation increased six fold in the north and central atlantic and pacific oceans and global changes in circulation lead to more diatomites in the pacific and fewer in the atlantic by the end of the miocene most of the mediterranean sea had evaporated broadly coincident with these events many old large river systems were destroyed and new ones formed as much of the world s landscape changed collectively these global on shore tectonic and ocean atmospheric events provide the foundation for our modern world a mixture of new and rejuvenated orogenic belts and their far field effects distant epiorogenic uplift rain shadow deserts large alluvial aprons and distant deltas as inherited gondwanan landscapes persisted remote from plate boundaries thus at the end of the miocene much of the world s landscape except for that changed by pleistocene continental glaciation would be recognizable to us today we argue that all of these events had the same ultimate common cause an internal earth engine that drove plate motions in two broad ways first the opening and closing of seven key gateways to deep water oceanic currents radically altered global heat transfer and changed a lingering greenhouse to an icehouse world secondly these events were in part coincident with renewed heat flow in the african and pacific superplumes that energized global plate motions in the middle and upper miocene we hope this global synthesis will stimulate more research on the many global events of the miocene to understand better both our modern world and earlier global orogenies

the effect of long term low temperature exposure on apatite fission track stability a natural annealing experiment in the deep ocean abstract since studies on deep sea cores were carried out in the early 1990s it has been known that ambient temperature may have a marked affect on apatite fission track annealing due to sluggish annealing kinetics this effect cannot be quantified by laboratory annealing experiments the unknown amount of low temperature annealing remains one of the main uncertainties for extracting thermal histories from fission track data particularly for samples which experienced slow cooling in shallow crustal levels to further elucidate these uncertainties we studied volcanogenic sediments from five deep sea drill cores that were exposed to maximum temperatures between 10 and 70 c over geological time scales of 15 120 ma mean track lengths mtl and etch pit diameters dpar of all samples were measured and the chemical composition of each grain analysed for age and track length measurements was determined by electron microprobe analysis thermal histories of the sampled sites were independently reconstructed based on vitrinite reflectance measurements and or 1d numerical modelling these reconstructions were used to test the most widely used annealing models for their ability to predict low temperature annealing our results show that long term exposure to temperatures below the temperature range of the nominal apatite fission track partial annealing zone results in track shortening ranging between 4 and 11 both chlorine content and dpar values explain the downhole annealing patterns equally well low chlorine apatite from one drill core revealed a systematic relation between si content and dpar value the question whether si substitution in apatite has direct and systematic effects on annealing properties however cannot be addressed by our data for samples which remained at temperatures 30 c the predictions of the laslett et al 1987 model agree with the measured mtl data within error levels with few exceptions predictions by the ketcham et al ketcham r donelick r and carlson w 1999 variability of apatite fission track annealing kinetics iii extrapolation to geological time scales am mineral 84 9 1235 1255 annealing model are consistent with the measured data for samples which remained at temperatures below 30 c for samples which experienced maximum temperatures between 30 and 70 c and which are rich in chlorine the ketcham et al 1999 model overestimates track annealing

mesozoic exhumation of the southern cape south africa quantified using apatite fission track thermochronology southern africa s topography is distinctive an inland plateau of low relief and high average elevation is separated from a coastal plane of high relief and low average elevation by a steeply dipping escarpment the origin and evolution of this topography is poorly understood because unlike high plateaus elsewhere its development cannot be easily linked to present day compressional plate boundary processes understanding the development of this regional landscape since the break up of gondwana is a first order step towards resolving regional epeirogenesis we present data that quantifies the timing and extent of exhumation across the southern cape escarpment and coastal plane using apatite fission track analysis afta of 25 outcrop samples and 31 samples from three deep boreholes kw1 67 sa1 66 cr1 68 outcrop fission track aft ages are cretaceous and are significantly younger than the stratigraphic ages of their host rocks indicating that the samples have experienced elevated paleotemperatures mean track lengths vary from 11 86 to 14 23 m the lack of cenozoic apatite ages suggests that major cooling was over by the end cretaceous the results for three boreholes situated seaward south of the escarpment indicate an episode of increased denudation in the mid late cretaceous 100 80 ma an earlier episode of increased denudation 140 120 ma is identified from a borehole north of the escarpment thermal modelling indicates a history involving 2 5 3 5 km of denudation in the mid late cretaceous 100 80 ma at a rate of 175 to 125 m ma the aft data suggest that less than 1 km of overburden has been eroded regionally since the late cretaceous 80 ma at a rate of 10 to 15 m ma but do not discount the possibility of minor in relative amplitude episodes of uplift and river incision through the cenozoic the reasons for rapid denudation in these early and mid cretaceous episodes are less clear but may be related to epeirogenic uplift associated with an increase in mantle buoyancy as reflected in two punctuated episodes of alkaline intrusions e g kimberlites across southern africa and contemporaneous formation of two large mafic igneous provinces 130 and 90 ma flanking its continental margins because cenozoic denudation rates are relatively minimal epeirogenic uplift of southern africa and its distinct topography cannot be primarily related to cenozoic mantle processes consistent with the lack of any significant igneous activity across this region during that time

intraseasonal periodicities in indian rainfall abstract spectral analysis of a 70 year 1901 70 record of daily precipitation from 3700 stations in the country of india is carried out to search for periodicities on subseasonal time scales during the summer monsoon two statistically significant spectral peaks are found a 40 50 day spectral peak corresponding to the madden julian oscillation is found over most of the portion of india south of 23 n the phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula ten to 12 days later the precipitation peaks simultaneously all along the coast west of the western ghats and along a line running across india between 20 and 25 n the precipitation maximum then spreads slowly northward and loses significance cross spectral analysis shows strong coherence between the precipitation patterns and wind oscillations the zonal wind oscillations at 850 and 200 mb am about 180 degrees out of phase equatorward of about 20 n but in pha

uranium occurrence state in the tarangaole area of the ordos basin china implications for enrichment and mineralization abstract the zhiluo formation in the tarangaole area is a part of the dongsheng uranium ore field in the northeast ordos basin china uraniferous sandstones from this formation are examined in this study the type and mode of occurrence of uranium minerals is investigated in detail using an electron probe track etching energy spectrum backscattering a scanning electron microscope and an experiment for sequential extraction of uranium the results show that these uranium minerals are mainly composed of coffinite a small amount of pitchblende and some minerals containing titanium and uranium coffinite closely coexists with pyrite altered ilmenite or leucoxene charcoal biotite and clay minerals some coffinite occurs along mineral edges as burrs or fine columns it also occurs in biotite cleavage cracks with granulars in addition some uranium minerals are also observed within grains track etching shows that adsorbed uranium is either distributed at the edge of the debris or scattered among the grains the sequential extraction experiment indicates that the proportion of uranium minerals was significantly greater than that of the adsorbed uranium in the samples with the latter being largely present in pyrite and organic matter residual oxidizable and weak acid extractable uranium occur in the deposit scan mapping of uranium and titanium reveales that brannerite is almost nonexistent strongly altered ilmenite is considered a highly effective aggregating agent for uranium a large number of altered minerals including clays carbonaceous clastics biotite pyrite and ilmenite are widely developed in the uraniferous sandstone and play a significant role in the complex process of adsorption reduction precipitation of uranium the discovery of pitchblende and two types of coffinite high y and low y are discussed in context with their symbiotic relationship with the altered minerals it is suggested that the uraniferous sandstone underwent at least two stages of fluid activity

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

chemical transfers along slowly eroding catenas developed on granitic cratons in southern africa abstract a catena is a series of distinct but co evolving soils arrayed along a slope on low slope slowly eroding catenas the redistribution of mass occurs predominantly as plasma the dissolved and suspended constituents in soil water we applied mass balance methods to track how redistribution via plasma contributed to physical and geochemical differentiation of nine slowly eroding 5 mm ky 1 granitic catenas the catenas were arrayed in a 3 3 climate by relief matrix and located in kruger national park south africa most of the catenas contained at least one illuviated soil profile that had undergone more volumetric expansion and less mass loss and these soils were located in the lower halves of the slopes by comparison the majority of slope positions were eluviated soils from the wetter climates 550 and 730 mm precipitation yr 1 generally had undergone greater collapse and lost more mass while soils in the drier climate 470 mm yr 1 had undergone expansion and lost less mass effects of differences in catena relief were less clear within each climate zone soil horizon mass loss and strain were correlated as were losses of most major elements illustrating the predominant influence of primary mineral weathering nevertheless mass loss and volumetric collapse did not become extreme because of the skeleton of resistant primary mineral grains inherited from the granite colloidal clay redistribution as traced by the ratio of ti to zr in soil suggested clay losses via suspension from catena eluvial zones thus illuviation of colloidal clays into downslope soils may be crucial to catena development by restricting subsurface flow there our analysis provides quantitative support for the conceptual understanding of catenas in cratonic landscapes and provides an endmember reference point in understanding the development of slowly eroding soil landscapes

late cretaceous cenozoic thermochronology in the southern songliao basin ne china new insights from apatite and zircon fission track analysis abstract the late cretaceous cenozoic thermochronology in the southern songliao basin was determined using apatite and zircon fission track analysis data it is crucial to deciphering the evolution of the songliao basin and changes in the movement direction of the pacific plate we present eight new apatite and eight corresponding zircon fission track data from borehole samples across the baixingtu uplift the apatite fission track aft thermochronological modeling reveals that the basin underwent two distinct compression and extension related uplift stages of rapid cooling during the late cretaceous cenozoic stage i during the late cretaceous early paleogene 70 52 ma stage ii in the late paleogene early neogene 38 10 ma the aft data vary from 76 0 5 0 to 25 3 1 9 ma and the zircon binomial peak fitting ages ranged from 79 to 61 ma all younger than the stratigraphic ages 92 88 ma of their host rocks one sample had similar fission track ages apatite 76 0 5 0 ma and zircon 79 0 3 0 ma within reasonable error representing a magmatic event the data were divided into four groups i 79 76 ma magmatic cooling event ii 69 61 ma uplift of the whole region and exhumation and erosion iii 37 34 ma and iv 25 ma various uplift events related to tectonic inversion causing partial uplift exhumation and erosion in the basin this created favorable conditions for formation and storage of mineral resources especially sandstone uranium ore deposits our results combined with previous research suggest that the variation in uplift and exhumation began in the basin s se part and propagated to the nw 5 8 ma later the tectonic inversion in the southern songliao basin at least began 37 34 ma this corresponds with the time of the paleo pacific plate shifting to nww motion and the india asia collision these regional scale uplift exhumation and inversion events were probably responses to the subduction and turning of the paleo pacific plate from the southeast and the collision of the indian subcontinent from the southwest it is important to study the tectonic inversion in the whole east of china since the late cretaceous and the change of the direction of the pacific plate movement

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

mineralogical and geochemical evidence for coupled bacterial uranium mineralization and hydrocarbon oxidation in the shashagetai deposit nw china unusual mineral structures have recently been found in a sandstone hosted roll type uranium deposit in the middle jurassic zhiluo formation in the shashagetai deposit the northern ordos basin nw china the structures possess a chemical composition and crystal structure characteristic of mineral coffinite usio4 1 x oh 4x which occurs as nanoparticles with size ranging from 5 to 25 nm these structures are interpreted to be fossilized microorganisms based on mineralogical biosignatures including morphology size occurrence of biogenic coffinite as nano crystals and biological elements such as p the intimate intergrowth of coffinite with secondary pyrite of bacterial origin as defined by low 34 s values and calcite cements with petroleum derived carbon supports its biogenic origin oil inclusions in the host sandstone are characterized by abundant n alkanes slightly increased pr nc17 and ph nc18 ratios significant amounts of demethylated hopanes and tricyclic terpanes and the existence of unresolved complex mixtures these characteristics are interpreted to be a result of mixing of an earlier heavily degraded oil with a later charged fresh oil subsequently the oils were slightly degraded these lines of evidence lead to the proposal that the reduction of sulfate and oxidization of petroleum are likely synchronous with reduction of hexavalent u vi to tetravalent u iv uranium by sulfate reducing bacteria srb the discovery of a natural association of microorganism like structures a uranium mineral and biodegraded petroleum has implications for uranium biomineralization and fossil fuel exploration

a linear inverse model of tropical and south pacific seasonal predictability a multivariate linear inverse model lim is developed to demonstrate the mechanisms and seasonal predictability of the dominant modes of variability from the tropical and south pacific oceans we construct a lim whose covariance matrix is a combination of principal components derived from tropical and extratropical sea surface temperature and south pacific ocean vertically averaged temperature anomalies eigen decomposition of the linear deterministic system yields stationary and or propagating eigenmodes of which the least damped modes resemble el nino southern oscillation enso and the south pacific decadal oscillation spdo we show that although the oscillatory periods of enso and spdo are distinct they have very close damping time scales indicating that the predictive skill of the surface enso and spdo is comparable the most damped noise modes occur in the midlatitude south pacific ocean reflecting atmospheric eastward propagating rossby wave train variability we argue that these ocean wave trains occur due to the high frequency atmospheric variability of the pacific south american pattern imprinting onto the surface ocean the enso spring predictability barrier is apparent in lim predictions initialized in march may mam but displays a significant correlation skill of up to 3 months for the spdo the predictability barrier tends to appear in june september jas indicating remote but delayed influences from the tropics we demonstrate that subsurface processes in the south pacific ocean are the main source of decadal variability and further that by characterizing the upper ocean temperature contribution in the lim the seasonal predictability of both enso and the spdo variability is increased

global miocene tectonics and regional sandstone style uranium mineralization abstract the formation of sandstone style uranium deposits are significantly controlled by the latest tectonic uplift events especially those generated in an open system by the infiltration of meteoritic water this study explores the spatiotemporal relationship between global miocene tectonics and sandstone style uranium deposits to evaluate the link between tectonic uplift and metallogenic ages in general modern landforms were shaped by diverse global tectonic events that began in the middle and late miocene this includes the formation of continental scale faults and fold belts including the uplift of the three broadly contemporaneous ranges the alpine himalayan belt the cordillera and the east african rift these events were accompanied by intense magmatic activity as well as an increase in the spreading rates of oceanic ridges and higher sedimentation rates in the pacific indian and atlantic oceans modern global climate patterns are a direct consequence of these miocene tectonic events studies on sandstone style uranium deposits report that though their stratigraphic ages extend from the proterozoic to the cenozoic they notably occur from the late mesozoic to the neogene uranium mineralization ages are concentrated between 20 and 0 1 ma clustering mainly in the miocene although remobilizations are known to have occurred subsequently some even in the holocene global tectonics in the miocene between 20 and 5 ma resulting in the regional uplift of mountain ranges and continental tilts may have exerted significant control over the migration directions of uranium bearing fluids that formed these sandstone style uranium deposits climate patterns in the miocene specifically subtropical high pressure belts on both sides of the equator controlled the creation of arid and semi arid areas creating characteristic rainfall patterns which would also have influenced the spatial distribution of these uranium deposits thus the spatiotemporal characteristics of most sandstone style uranium deposits in the world were controlled by global tectonics in the miocene that uplifted mountain ranges and tilted continents generating subtropical high pressure belts and the asian high pressure region in addition to new ideas adding greater research value to the study of global sandstone style uranium mineralization this paper also provides a new exploration indicator for sandstone style uranium deposits

fission track analysis of the crystalline basement rocks of the calabrian arc southern italy evidence of oligo miocene late orogenic extension and erosion abstract fission track analysis is used to provide low temperature and time constraints on the late orogenic cooling and exhumational history of the crystalline basement rocks of the calabrian arc southern italy 65 samples yielded 57 apatite fission track ages 54 zircon fission track ages and 25 apatite confined fission track length distributions interpretation of this data reveals a phase of increased cooling rates related to exhumation between approximately 35 ma mid oligocene and 15 ma middle miocene evidence from the sedimentary record indicates significant oligo miocene erosion related to this period of exhumation new chronological constraints are also applied to localised late orogenic extensional tectonism that has recently been identified within the basement rocks of the calabrian arc this information is used to produce a new model of the oligo miocene tectonic evolution of the calabrian arc it proposes that the crystalline basement rocks were part of a critical orogenic wedge between the mid oligocene and the middle miocene

geochronological evidence for pervasive miocene weathering minas gerais brazil ar 40 ar 39 laser incremental heating analyses of 22 individual grains of supergene cryptomelane from three weathering profiles up to 400 km apart in the rio doce valley and barbacena regions at minas gerais brazil show that the formation of weathering profiles in these regions is contemporaneous suggesting a strong weathering event in the middle to late miocene 10 8 ma the preservation of these miocene samples at or near the present surface suggests that either erosion rates have been very low in the region since the miocene or that a much thicker weathering mantle was present in the region originally assuming a constant thickness of weathering profiles in the region throughout the tertiary we may calculate weathering front propagation rates of 4 8 m myr 1 during the past 10 ma copyright c 2004 john wiley sons ltd

the temporal evolution of the active margin along the southeast anatolian orogenic belt se turkey evidence from u pb ar ar and fission track chronology abstract the southeast anatolian orogenic belt saob resulted from the north dipping subduction of the southern neotethyan oceanic lithosphere in late mesozoic and early cenozoic however the timing and the rate of the continental collision are still under debate here we present new u pb ar ar and fission track ages from the i type calc alkaline granitoids esence dogansehir and baskil cutting the goksun ispendere and komurhan ophiolites and also the malatya keban metamorphics representing the tauride active continental margin along the saob in this study high to low temperature thermochronological methods applied to the granitoids are used to understand the temporal and geodynamic evolution of the tauride active continental margin and continental collision between tauride and arabian platforms in the frame of the neotethyan convergence during cretaceous and miocene the u pb zircon ages range from 83 to 88 ma for the baskil and from 81 to 83 ma for the esence granitoids the 39 ar 40 ar ages indicate that these late cretaceous granitoids cooled below 300 c in 6 10 ma the formation ages and the timing of the gradual cooling of the late cretaceous granitoids are similar to metamorphism age and the timing of the exhumation of the hp lt bitlis metamorphics during this stage the combined field geochemistry and geo thermochronological data suggest that the first continental collision event occurred between bitlis puturge micro continents to the south and tauride platform to the north in an oblique subduction zone between 84 and 74 ma the granitoids continued uplifting during early middle eocene together with the exhumation of hp uht berit metaophiolite in an extensional regime related to the opening of the maden back arc basin this period also let the intrusion of the dogansehir arc magmatism intruding the puturge and malatya keban metamorphics berit metaophiolite and maden complex the eocene dogansehir granitoid has similar u pb and 39 ar 40 ar ages suggesting a fast cooling the apatite fission track aft ages for all granitoid bodies suggest that they were mainly cooled or uplifted in two episodes where the first one is in the eocene in an extensional setting the aft data marked the final continental collision between the taurides and the arabian platform first in oligocene and the break off of the subducted slab and the delamination process caused fast uplift of the eastern anatolia during middle to late miocene

insights into extensional events in the betic cordilleras southern spain new fission track and u pb shrimp analyses abstract a combination of the u pb shrimp and zircon fission track analyses has been used to constrain the age and evolution of the extensional tectonics in the betic cordilleras southern spain the studied rocks are dolerite dykes intruded in the malaguide complex and in the underlying los reales nappe and their country rocks the dykes are grouped in two nearly perpendicular systems characterized by n s strikes in the los reales nappe and e w strikes in the malaguide complex two periods of extension have been identified the age of the older event ranging from 33 to 25 ma is constrained by the intrusion of the dykes 33 ma and the joint cooling of the los reales malaguide domain from 25 ma onwards this event is associated with the structural emplacement of the malaguide complex over the los reales nappe along a brittle ductile extensional detachment and is tentatively ascribed to the tectonic collapse of the orogenic belt a minimum time span of 10 m y is established between the onset of the extensional collapse and the widespread aquitanian ht lp metamorphism in the present geographic frame the kinematics of this event is characterized by a change from an e w extension at lower levels los reales nappe to a n s extension in upper levels malaguide complex a younger extensional event of miocene age 18 ma has been deduced based on the fission track analysis within the calizas alabeadas member of the malaguide complex

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

regional sandstone type uranium mineralization rooted in oligo miocene tectonic inversion in the songliao basin ne china abstract the tectonic inversion of the songliao basin during the oligo miocene may have played an important role in controlling the development of sandstone type uranium deposits suds here we investigate drill holes along a southeast to northwest section in this basin based on apatite fission track aft and zircon fission track zft techniques we present 50 data from 15 deep boreholes at different depths between 665 and 3956 m and different structural units including grabens and horsts formed in the early cretaceous beneath the basin the results of the effective aft ages are 100 11 to 2 3 0 4 ma p x2 5 and zft ages are 97 5 20 4 ma including binomial peak ages these results reveal that the basin underwent two distinct stages of rapid cooling after late cretaceous in the first stage during the late cretaceous early paleogene 80 50 ma tectonic uplift occurred in all of the structural units including grabens and horsts which was marked by an unconformity between the latest cretaceous mingshui and the eocene yi an formations in the second stage during the oligo miocene 40 10 ma tectonic uplift occurred mainly in the grabens but not in the horsts corresponding with a few sediments of the neogene da an and taikang formations we propose that the folds and the thrust faults mostly characterize in the second stage indicating a major tectonic inversion in the basin the shifting of the two stages was probably in response to differences in the subduction angles and directions of motion of the paleo pacific plate from the southeast combined with previous information it was demonstrated that most of the u mineralization ages are younger than 40 ma with a peak in the miocene or later

post break up tectonic inversion across the southwestern cape of south africa new insights from apatite and zircon fission track thermochronometry the south west african margin is regarded as an example of a passive continental margin formed by continental rifting following a phase of lithospheric extension and thinning recent attention focused on this margin has included theoretical modelling studies of rift processes plate kinematic studies of the opening geometry and timing and empirical studies focused on documenting the crustal structure and offshore sedimentary record here we examine the onshore geomorphic and tectonic response to rifting and breakup with a specific focus on the sw cape of south africa we present 75 new apatite and 8 new zircon fission track analyses from outcrop samples and onshore borehole profiles along the western margin of south africa the data are used to derive robust thermal histories that record two discrete phases of accelerated erosional cooling during the early cretaceous 150 130 ma and late cretaceous 100 80 ma respectively both periods of enhanced erosion are regional in extent involved km scale erosion and extend well inland of the current escarpment zone albeit with spatially variable intensity and style the late cretaceous episode is also expressed more locally by tectonic reactivation and inversion of major faults causing km scale differential displacement and erosion the new aft data do not exclude the possibility of modest surface uplift occurring during the cenozoic but they restrict the depth of regional cenozoic erosion on the western margin to less than c 1 km the inferred pattern and chronology of erosion onshore is consistent with the key features and sediment accumulation patterns within the offshore orange and bredasdorp basins it is suggested that the late cretaceous event was triggered by a combination of regional dynamic uplift augmented along the western margin and in the sw cape by local tectonic forces arising from dextral displacement of the falkland plateau along the falkland agulhas fracture zone

principal oscillation pattern analysis of the 30 to 60 day oscillation in the tropical troposphere the principal oscillation pattern technique is used to derive an index of the 30 to 60 day oscillation in the tropical troposphere in the 200 mb equatorial velocity potential field one dominant pair of pops is found its properties compare very well with the properties of the oscillation identified in previous studies in particular a good correlation between the time evolution of the pop coefficients and area averaged outgoing long wave radiation orl is found the pops are derived from a 2 year subinterval of the whole 5 year data set this leaves independent data for subsequent verification the patterns and their characteristic numbers are almost unchanged if the whole data set is analysed also the analysis is insensitive to changes of the analysis area if the analysis is limited to 90 longitude equatorial sectors the signal is also identified and its patterns are consistent with the patterns derived from the full data set interestingly the signal is best defined in the eastern hemisphere the pops may be used to derive associated correlation patterns of other quantities in winter and summer separately the path of the oscillation has a marked annual cycle in northern winter it migrates from the indian ocean across northern australia into the region of the south pacific convergence zone spcz and in northern summer it moves from the indian ocean across south asia along the intertropical convergence zone itcz to south america the pop coefficient may be seen as a bivariate index of the state phase and strength of the 30 to 60 day oscillation since the pop technique incorporates a prediction equation for the phase of the pop coefficients the pop model allows for the prediction of the complex amplitude of the oscillation in a sequence of forecast experiments of which about two thirds used independent data the pop forecasts were found to be useful in about half of all cases for lead times of several days the correlation and rms skills were calculated for the pop forecast and for persistence the pop forecast appears to be considerably better with respect to both measures the correlation skill scores 60 after 7 days the pop forecast is most skillful in northern winter and if strong signals are present with minima of velocity potential in the eastern hemisphere

planation surfaces as a record of mantle dynamics the case example of africa abstract there are two types of emerged relief on the earth high elevation areas mountain belts and rift shoulders in active tectonic settings and low elevation domains anorogenic plateaus and plains characteristic of the interior of the continents i e 70 of the earth emerged relief both plateaus and plains are characterized by large erosional surfaces called planation surfaces that display undulations with middle several tens of kilometres to very long several thousands of kilometres wavelengths i e characteristic of lithospheric and mantle deformations respectively our objective is here 1 to present a new method of characterization of the very long and long wavelength deformations using planation surfaces with an application to central africa and 2 to reconstruct the growth of the very long wavelength relief since 40 ma as a record of past mantle dynamics below central africa i the african relief results from two major types of planation surfaces etchplains weathering surfaces by laterites and pediplains pediments these planation surfaces are stepped along plateaus with different elevations this stepping of landforms records a local base level fall due to a local tectonic uplift ii central africa is an extensive etchplain type weathering surface called the african surface from the uppermost cretaceous 70 ma to the middle eocene 45 ma with a paroxysm around the early eocene climatic optimum restoration of this surface in central africa suggests very low elevation planation surfaces adjusted to the atlantic ocean and indian ocean with a divide located around the present day eastern branch of the east african rift iii the present day topography of central africa is younger than 40 30 ma and records very long wavelength deformations 1000 2000 km with 1 the growth of the cameroon dome and east african dome since 34 ma 2 the angola mountains since 15 12 ma increasing up to pleistocene times and 3 the uplift of the low elevation 300 m congo basin since 10 3 ma some long wavelength deformations several 100 km also occurred with 1 the low elevation central african rise since 34 ma and 2 the atlantic bulge since 20 16 ma these very long wavelength deformations record mantle dynamics with a sharp increase of mantle upwelling around 34 ma and an increase of the wavelength of the deformation and then of mantle convection around 10 3 ma

cenozoic tectonic evolution of liaodong dome northeast liaodong bay bohai offshore china constraints from seismic stratigraphy vitrinite reflectance and apatite fission track data abstract the liaodong dome is a region of localized uplift and deformation within the liaodong bay bohai offshore china 3 d seismic dataset vitrinite reflectance and apatite fission track data provide an exceptional opportunity to document the evolution of the liaodong dome which developed coeval with the tan lu strike slip fault zone with a rift system the 3 d seismic data demonstrates that the dome formed before the deposition stage of esm sequence 40 ma and it uplifted again during or after the depositional stage of ed sequence 32 24 ma apatite fission track and vitrinite reflectance data indicate that the dome experienced two stages of cooling episodes paleocene to early middle eocene 65 40 ma and late oligocene to late miocene 30 11 5 ma usually indicating uplifting both the seismic stratigraphy and thermal history analysis show that 1 the liaodong dome is part of the jiaoliao terrane 2 regional continental rifting climaxed during 65 40 ma as it did the rift shoulder uplift of the dome 3 the reactivation of the tan lu fault caused a second uplift processes of the liaodong dome during 30 11 5 ma 4 the liaodong dome uplifted independently and separated from the jiaoliao terrane our results also suggest that it is important to take uplifting evolution into consideration to target a potential petroleum reservoir

u pb ages of uranium ores in the churchrock uranium district new mexico examines samples from the largest us uranium producing region in order to determine ages of mineralization of different orebodies uranium from this area has come mainly from arkosic and subarkosic sandstones of the upper jurassic morrison formation several lines of evidence suggest that ages range from late jurassic or early cretaceous to at least as young as tertiary geologic observations indicate that the oldest primary orebodies are tabular in shape and rich in amorphous organic material whereas the youngest orebodies tend to be poor in amorphous organic material display roll front geometry and are commonly spatially associated with laramide or younger faults both types of ore were formed by relatively lowtemperature dilute fluids that were essentially ground water in nature concludes that the 0 to 1 m y u pb apparent ages of the united nuclear corporation church rock mine relate to redistribution by roll front processes of earlier formed ores by oxidizing pleistocene ground waters perhaps those that resulted in the present day limonitic zone of the westwater canyon member suggests that the 10 m y apparent age of sample km 17 1 may represent an earlier phase of redistributed ore formation perhaps related to the tertiary oxidation front that resulted in the present day hematitic zone of the westwater canyon member

rise of the andes the surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening leading to their gradual rise recent studies of the andes indicate that their elevation remained relatively stable for long periods tens of millions of years separated by rapid 1 to 4 million years changes of 1 5 kilometers or more periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable dense lower lithosphere after long term thickening of the crust and lithospheric mantle

selective crystallization and precipitation of authigenic pyrite during diagenesis in uranium reservoir sandbodies in ordos basin abstract the occurrence characteristics of authigenic pyrite during diagenesis in uranium reservoir sandbodies of zhiluo formation in ordos basin are investigated based on outcrop area investigations and drilled cores observations the pyrite is closely related to carbonaceous debris microscopically the host components for pyrite consist of carbonaceous debris clay minerals biotite the earlier pyrite and ilmenite by emphasizing on 34s values via la icp ms as well as observing through optical microscope and scanning electron microscope equipped with energy dispersive spectroscope three kinds of distribution pattern of pyrite are classified as i periphery ii infilling iii the combined form of the above two in situ micrometer scale sulfur isotope analyses of pyrite demonstrated that broad scale isotopes are heterogeneous from 52 5 to 35 4 of 34s and sulfur is derived from more than a single source significant differences of host components effects on authigenic pyrite formation are discussed the carbonaceous debris can supply the energy for the bacterial sulfate reduction process and the biotite can provide the source of iron for pyrite precipitation the ferrous ion can be adsorbed on the surface of the clay minerals meanwhile the authigenic pyrite is distributed in or around the earlier pyrite and ilmenite by the indirect adsorption of ferrous ion and the ilmenite may also provide the source of iron futhermore the uranium minerals are mainly associated with the authigenic pyrite relevant to carbonaceous debris and clay minerals which indicates there exists constraints of authigenic pyrite during diagenesis on the uranium mineralization

shaping post orogenic landscapes by climate and chemical weathering the spacing of hills and valleys reflects the competition between disturbance driven or diffusive transport on hillslopes and concentrative or advective transport in valleys although the underlying lithologic tectonic and climatic controls have not been untangled here we measure geochemical and geomorphic properties of catchments in kruger national park south africa where granitic lithology and erosion rates are invariant enabling us to evaluate how varying mean annual precipitation map 470 mm 550 mm and 730 mm impacts hill valley spacing or landscape dissection catchment averaged erosion rates based on 10be concentrations in river sands are low 3 6 m m y and vary minimally across the three sites our lidar derived slope area analyses reveal that hillslopes in the dry site are gentle 3 and short such that the terrain is low relief and appears highly dissected with increasing rainfall hillslopes lengthen and increase in gradient 6 8 resulting in less dissected higher relief catchments the chemical depletion fraction of hilltop regoliths increases with rainfall from 0 3 to 0 7 reflecting a climate driven increase in chemical relative to physical erosion soil catenas also vary systematically with climate as we observe relatively uniform soil properties in the dry site that contrast with leached sandy crests and upper slopes coupled with downslope clay accumulation zones in the intermediate and wet sites the geomorphic texture of this slow eroding granitic landscape appears to be set by climate driven feedbacks among chemical weathering regolith fabric differentiation hydrological routing and sediment transport that enhance the vigor of hillslope sediment transport relative to valley forming processes for wetter climates 2013 geological society of america

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

onshore and offshore apatite fission track dating from the southern gulf of california insights into the time space evolution of the rifting abstract we present the results of a apatite fission track aft study on intrusive rocks in the southern gulf of california sampled along the eastern margin of baja california sur western rift margin as well as from islands and submerged rifted blocks within the gulf of california and from the conjugate mexican margin nayarit state for most of the samples u pb zircon and 40ar 39ar mineral ages were already available duque trujillo et al 2015 coupled with the new aft data these ages provide a more complete information on cooling after emplacement our samples span a wide range of ages between 5 5 1 1 and 73 7 5 8 ma and show a general spatial distribution with late miocene aft ages about 6 ma aligned roughly nw se along a narrow offshore belt parallel to baja california peninsula separating older ages on both sides this pattern suggests that in late miocene deformation due to plate transtension focused at the eastern rheological boundary of the baja california block some early miocene aft ages onshore baja california could be related to plutons emplaced at shallow depths and thermal resetting associated with the onset of volcanism at 19 ma in this part of the peninsula on the other hand an early extensional event similar to that documented in the eastern gulf cannot be ruled out in the westernmost baja california

eocene to pliocene exhumation history of the tianshui huicheng region determined by apatite fission track thermochronology implications for evolution of the northeastern tibetan plateau margin abstract this study presents new apatite fission track aft data from the tianshui huicheng region which is situated in the northeastern margin of the tibetan plateau aft results including 19 detrital and 13 bedrock samples show that deposition in the tianshui huicheng basin range from early eocene to late miocene pliocene and most of the apatites derived from the western qinling orogenic belt reflecting one rapid exhumation episode at 34 29 ma and two phases of volcanism at 23 18 ma and ca 13 ma the exhumation history of the tianshui huicheng region is likely related to episodic tectonic activity and directly linked to the kinematics of active deformation of the tibetan plateau active processes deciphered from the detritus indicate that deformation reached the northeastern tibetan plateau margin as early as ca 49 ma which is manifested by the initiation of the tianshui huicheng basin the 23 18 ma event linked to the lithosphere deformation of the western qinling and the neogene basin formation along the tianshui huicheng region by modeling the bedrock samples an 8 4 ma event was revealed which resulted from the intense deformation of the tianshui huicheng region

three dimensional structure and evolution of the mjo and its relation to the mean flow abstractthe two leading principal components of the daily 850 minus 150 hpa global velocity potential in the interim european centre for medium range weather forecasts ecmwf re analysis era interim 1979 2011 data are used as time varying madden julian oscillation mjo indices regression maps and meridional cross sections based on these indices are used to document the structure and evolution of the zonal wind u and geopotential height z anomalies in the mjo cycle the data are daily and they are not separated by season at upper tropospheric levels the mjo signature is dominated by eastward propagating planetary wave packets consisting of equatorial kelvin waves flanked by rossby waves centered along 28 n s for which the westerly jet streams serve as waveguides at lower tropospheric levels the pattern more closely resembles the response to a pulsating heat source over the maritime continent where the andes block the eastward propagating kelvin wave pulse the contrasting upper and lower

passive margin uplift around the north atlantic region and its role in northern hemisphere late cenozoic glaciation tectonic climatic models of late cenozoic global cooling emphasize the importance of middle latitude uplifts e g tibetan plateau and the american west but ignore widespread tectonic events on the margins of the north atlantic ocean pleistocene glaciations after 2 5 ma are characterized by circum north atlantic continental ice sheets that formed by the coalescence of perennial snow fields on extensive plateau surfaces in eastern canada northwest britain and scandinavia plateaus record cenozoic uplift of peneplains in response to semisynchronous magmatic underplating and thermal buoyancy of rifted continental margins high standing plateaus are very sensitive to small reductions in summer temperature as late cenozoic climate cooling proceeded driven by uplift in regions external to the north atlantic region elevated plateaus became sites for extensive snow fields and ultimately ice sheets circum atlantic uplift took place in the key latitudinal belt that is most sensitive to orbitally forced changes in solar irradiation this together with albedo effects from large snow fields could have amplified the relatively weak milankovitch signal

geochemical consequences of increased late cenozoic weathering rates and the global co2 balance since 100 ma large imbalances in the relative net co2 flux over the last 100 m y are obtained from independently derived estimates of co2 uptake by weathering and organic carbon burial and of co2 outgassing assumed proportional to the mean mid ocean ridge mor spreading and mantle plume production mpp rates increasing the river flux of ca mg p and c by 50 since 30 ma to parallel the proposed increase in the sr river flux needed to explain the sr isotopic evolution of seawater richter et al 1992 has a large impact on the global carbon cycle by reducing the excess net co2 imbalance in the late cenozoic co2 uptake is calculated by assuming that 19 of the ca river flux and 60 of the mg river flux are derived from weathering silicates and that mg is removed in the oceans by 1 1 molar exchange reactions with calcsilicates an increase in the mg river flux combined with an overall decrease in the mor spreading rate predicts as much as a factor of 2 increase in the seawater mg concentration since 100 ma the net organic carbon burial flux burial minus weathering largely reflects changes in the bulk carbonate 13c record and to a lesser extent variations in the net carbonate burial flux and mean 13c value of the carbonate weathering flux organic carbon burial efficiency is markedly less than that of p from the middle middle miocene to the present because of early diagenetic transfer of organic p to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations the large co2 imbalance of the late cretaceous requires significantly less carbonate subduction or greater weathering rates a co2 balance can be achieved in the miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted variations in shallow water carbonate burial and hence the global carbonate record are currently too poorly known to differentiate between the above possibilities the decrease in the excess co2 flux generally parallels the trend to cooler climate inferred from the 18o record but periods of large co2 imbalance generally precede 18o shifts by several million years

the miocene pliocene boundary and the messinian salinity crisis in the easternmost mediterranean insights from the hatay graben southern turkey accepted manuscript version published version at http dx doi org 10 1016 j sedgeo 2015 11 012 license in accordance with the journal s policy cc by nc nd

the deep record of the messinian salinity crisis evidence of a non desiccated mediterranean sea abstract this research is focused on a complete reexamination of the evaporite facies present in all the cores that cut through the topmost deposits of the messinian salinity crisis lying below the floor of the mediterranean sea dsdp legs 13 and 42a odp legs 107 and 161 this review suggests that the uppermost evaporite units in both western and eastern deep mediterranean basins consist mainly of clastic gypsrudite gypsarenite and gypsiltite and fully subaqueous deposits laminar gypsum selenite and cumulate halite that are partially affected by burial anhydritization and tectonic induced recrystallization no unequivocal evidence of shallow water or even supratidal sabkha deposition is in evidence suggesting that at the very last phase of the salinity crisis the mediterranean sea did not experience desiccation but that deposition took place under permanent subaqueous conditions

oblique to orthogonal convergence across the turan block in the post miocene the 2 17 km thick post triassic sediments of the turan continental block accumulated in a south dipping basin characterized by fault controlled facies and thickness variations since the late miocene the thickest part of the basin fill on the southern margin of the turan block has been folded and uplifted as the kopet dag range in response to the iran turan convergence the apsheron sill which separates the northern continental from the southern oceanic caspian sea basins links the kopet dag greater balkan ranges turkmenistan to the caucasus azerbaijan the large scale east west to west northwest east southeast oriented arrays of periclinal folds of the kopet dag range which indicate a north south oriented compression were generated by a fault propagation mechanism the migration and accumulation of hydrocarbons has been controlled by the deformation pattern the 75 km of north south shortening in the western kopet dag greater balkan area can be resolved into 70 km of pure compression orthogonal to the n120 oriented ashgabat fault and 35 km of dextral slip along this fault the north south iran asia relative motion has produced the oblique convergent northwest southeast structures along the dextral ashgabat fault and the pure convergent east west structures in the western kopet dag greater balkan region the orientation of the structures has been controlled by the angular relationship between the relative motion of two blocks and the orientation of their boundaries the ashgabat fault as a major crustal anisotropy has concentrated the deformation into a narrow fold and thrust belt whereas in the west the deformation is distributed over a wider area the pattern of deformation has been controlled by the iran turan boundary conditions

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

the madden julian oscillation in the canadian climate centre general circulation model the madden julian oscillation mjo simulated by the canadian climate centre general circulation model ccc gcm is identified by a principal oscillation pattern pop analysis and compared with that observed in the real atmosphere the results are based upon two integrations of the ccc gcm one with a parameterization of penetrative cumulus convection exp1 and the other with a moist convective adjustment scheme exp2 the signal of mjo can be detected in both integrations as the first pop of the 200 hpa velocity potential along the equator the disturbances show a distinctive wave number one structure with the strongest local amplitude found in the longitudes corresponding to the region of the asian monsoon the phase speed of the eastward wave propagation is higher in the eastern pacific and lower in the monsoon region where the convective activities are strongest these features are in good agreement with the observations the energy spectrum of the velocity potential peaks at the frequency corresponding to a period of about 38 days for exp1 which is somewhat shorter compared to the observed periods of 40 50 days on the other hand two spectral peaks can be clearly identified for exp2 one with a period of 24 days and the other with a much longer period somewhere near 112 days both peaks appear statistically significant at 95 level long term data of the observed atmosphere show little indication of such spectral separation the horizontal patterns identified by the pop analysis resemble to some extent the baroclinic response of tropical flow to a heat source travelling with the speed of mjo at the upper level rossby wave energy propagates westward with winds generally following the height contours whereas kelvin wave energy propagates to the east from the heat source with strong cross contour flow near the equator at the lower level the patterns are essentially reversed the model generated precipitation and diabatic heating are examined by compositing against the moving mjo it is found in exp2 that the composite heating distribution is coherent with the flow pattern only in a certain sector of the equator depending on whether the fast or slow mode is used to determine the reference point the composite vertical heating profile of a slower mode tends to have a maximum found at a lower level the sensitivity of simulated mjo to the cumulus convection scheme in the model is discussed

the linear response of enso to the madden julian oscillation the possibility that the tropical pacific coupled system linearly amplifies perturbations produced by the madden julian oscillation mjo is explored this requires an estimate of the low frequency tail of the mjo using 23 yr of ncep ncar reanalyses of surface wind and reynolds sst we show that the spatial structure that dominates the intraseasonal band i e the mjo also dominates the low frequency band once the anomalies directly related to enso have been removed this low frequency contribution of the intraseasonal variability is not included in most enso coupled models used to date its effect in a coupled model of intermediate complexity has therefore been studied it is found that this mjo forcing mjo can explain a large fraction of the interannual variability in an asymptotically stable version of the model this interaction is achieved via linear dynamics that is it is the cumulative effect of individual events that maintains ensos in this model the largest coupled wind anomalies are initiated after a sequence of several downwelling kelvin waves of the same sign have been forced by mjo the cumulative effect of the forced kelvin waves is to persist the small sst anomalies in the eastern pacific just enough for the coupled ocean atmosphere dynamics to amplify the anomalies into a mature enso event even though mjo explains just a small fraction of the energy contained in the stress not associated with enso a large fraction of the modeled enso variability is excited by this forcing the characteristics that make mjo an optimal stochastic forcing for the model are discussed the large zonal extent is an important factor that differentiates the mjo from other sources of stochastic forcing

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

genetic and grade and tonnage models for sandstone hosted roll type uranium deposits texas coastal plain usa abstract the coincidence of a number of geologic and climatic factors combined to create conditions favorable for the development of mineable concentrations of uranium hosted by eocene through pliocene sandstones in the texas coastal plain here 254 uranium occurrences including 169 deposits 73 prospects 6 showings and 4 anomalies have been identified about 80 million pounds of u 3 o 8 have been produced and about 60 million pounds of identified producible u 3 o 8 remain in place the development of economic roll type uranium deposits requires a source large scale transport of uranium in groundwater and deposition in reducing zones within a sedimentary sequence the weight of the evidence supports a source from thick sequences of volcanic ash and volcaniclastic sediment derived mostly from the trans pecos volcanic field and sierra madre occidental that lie west of the region the thickest accumulations of source material were deposited and preserved south and west of the san marcos arch in the catahoula formation by the early oligocene a formerly uniformly subtropical climate along the gulf coast transitioned to a zoned climate in which the southwestern portion of texas coastal plain was dry and the eastern portion humid the more arid climate in the southwestern area supported weathering of volcanic ash source rocks during pedogenesis and early diagenesis concentration of uranium in groundwater and movement through host sediments during the middle tertiary era abundant clastic sediments were deposited in thick sequences by bed load dominated fluvial systems in long lived channel complexes that provided transmissive conduits favoring transport of uranium rich groundwater groundwater transported uranium through permeable sandstones that were hydrologically connected with source rocks commonly across formation boundaries driven by isostatic loading and eustatic sea level changes uranium roll fronts formed as a result of the interaction of uranium rich groundwater with either 1 organic rich debris adjacent to large long lived fluvial channels and barrier bar sequences or 2 extrinsic reductants entrained in formation water or discrete gas that migrated into host units via faults and along the flanks of salt domes and shale diapirs the southwestern portion of the region the rio grande embayment contains all the necessary factors required for roll type uranium deposits however the eastern portion of the region the houston embayment is challenged by a humid environment and a lack of source rock and transmissive units which may combine to preclude the deposition of economic deposits a grade and tonnage model for the texas coastal plain shows that the texas deposits represent a lower tonnage subset of roll type deposits that occur around the world and required aggregation of production centers into deposits based on geologic interpretation for the purpose of conducting a quantitative mineral resource assessment

increasing nd isotopic ratio of asian dust indicates progressive uplift of the north tibetan plateau since the middle miocene the time and rate of tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change models predict that the uplift of the north tibetan plateau ntp occurred later than uplift of the south and central tibetan plateau uplift of the ntp is believed to have initiated the aridity in the interior of asia and to have critically affected the evolution of asian monsoon and ultimately global climate the history of ntp uplift has remained uncertain however scenarios range from early miocene to the past million years this work provides new evidence by relating the nd isotopic evolution of asian dust to ntp uplift the sources of the asian dust are located in the arid lands between the ntp and the central asia orogen mass balance calculations indicate that the decreasing e nd values from 8 2 to 10 4 for pacific dust since 15 ma reflects increasing relative contribution of ntp materials 40 to 70 to the dust source as paleoelevation in the central asia orogen has largely remained constant the increasing relative ntp detritus contribution is interpreted to reflect the progressive surface uplift of the ntp at a rate of at least 0 12 mm yr 1 since 15 ma

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

the sandstone hosted beverley uranium deposit lake frome basin south australia mineralogy geochemistry and a time constrained model for its genesis the sandstone hosted beverley uranium deposit is located in terrestrial sediments in the lake frome basin in the north flinders ranges south australia the deposit is 13 km from the u rich mesoproterozoic basement of the mount painter inlier which is being uplifted 100 to 200 m above the basin by neotectonic activity that probably initiated in the early pliocene the mineralization was deposited mainly in organic matter poor miocene lacustrine sands and partly in the underlying reductive strata comprising organic matter rich clays and silts the bulk of the mineralization consists of coffinite and or uraninite nodules growing around co rich pyrite with an s isotope composition 34 s 1 0 0 3 suggestive of an early diagenetic lacustrine origin in contrast authigenic sulfides in the bulk of the sediments have a negative s isotope signature 34 s ranges from 26 2 to 35 5 indicative of an origin via bacterially mediated sulfate reduction minor amounts of zn bearing native copper and native lead also support the presence of specific reducing microenvironments in the ore zone small amounts of carnotite are associated with the coffinite ore and also occur beneath a paleosoil horizon overlying the uranium deposit provenance studies suggest that the host miocene sediments were derived from the reworking of early cretaceous glacial or glaciolacustrine sediments ultimately derived from paleozoic terranes in eastern australia in contrast the overlying pliocene strata were in part derived from the mesoproterozoic basement inlier mass balance and geochemical data confirm that granites of the mount painter domain were the ultimate source of u and ree at beverley u pb dating of coffinite and carnotite suggest that the u mineralization is pliocene 6 7 3 4 ma the suitability of the beverley deposit for efficient mining via in situ leaching and hence its economic value are determined by the nature of the hosting sand unit which provides the permeability and low reactivity required for high fluid flow and low chemical consumption these favorable sedimentologic and geometrical features result from a complex conjunction of factors including deposition in lacustrine shore environment reworking of angular sands of glacial origin deep pliocene weathering and proximity to an active fault exposing extremely u rich rocks

a refinement of the chronology of rift related faulting in the broadly rifted zone southern ethiopia through apatite fission track analysis to reconstruct the timing of rift inception in the broadly rifted zone in southern ethiopia we applied the fission track method to basement rocks collected along the scarp of the main normal faults bounding i the amaro horst in the southern main ethiopian rift and ii the beto basin in the gofa province at the amaro horst a vertical traverse along the major eastern scarp yielded pre rift ages ranging between 121 4 15 3 ma and 69 5 7 2 ma similarly to two other samples one from the western scarp and one at the southern termination of the horst 103 4 24 5 ma and 65 5 4 2 ma respectively more interestingly a second traverse at the amaro northeastern terminus released rift related ages spanning between 12 3 2 7 and 6 8 0 7 ma in the beto basin the ages determined along the base of the main northwestern fault scarp vary between 22 8 3 3 ma and 7 0 0 7 ma we ascertain through thermal modeling that rift related exhumation along the northwestern fault scarp of the beto basin started at 12 2 ma while in the eastern margin of the amaro horst faulting took place later than 10 ma possibly at about 8 ma these results suggest a reconsideration of previous models on timing of rift activation in the different sectors of the ethiopian rift extensional basin formation initiated more or less contemporaneously in the gofa province 12 ma and northern main ethiopian rift 10 12 ma at the time of a major reorganization of the nubia somalia plate boundary i e 11 2 ma afterwards rift related faulting involved the southern mer amaro horst at 8 ma and only later rifting seemingly affected the central mer after 7 ma

petrography and geochemistry of granitoids from the samphire pluton south australia implications for uranium mineralisation in overlying sediments abstract the blackbush uranium deposit jorc inferred resource 12 580 tonnes u located on the north eastern eyre peninsula is currently the only sediment hosted u deposit investigated in detail in the gawler craton uranium is hosted within eocene sandstone of the kanaka beds overlying mesoproterozoic granites of the samphire pluton affiliated with the hiltaba intrusive suite 1 6 ga these are considered the most probable source rocks for uranium mineralisation by constraining the petrography and mineralogy of the granites insights into the post emplacement evolution can be gained which may provide an exploration indicator for other sediment hosted uranium systems three geochemically distinct granite types were identified in the samphire pluton and correspond to domains interpreted from geophysical data all granites show complex alteration overprints and textures with increasing intensity closer to the deposit as well as crosscutting veining alkali feldspar has been replaced by porous k feldspar and albite and plagioclase is overprinted by an assemblage of porous albite sericite calc silicates prehnite pumpellyite and epidote this style of feldspar alteration is regionally widespread and known from hiltaba aged granites associated with iron oxide copper gold mineralisation at olympic dam and in the moonta wallaroo region in two granite types biotite is replaced by calcic garnet calc silicates are indicative of ca metasomatism sourced from the anorthite component of altered plagioclase minor clay alteration of feldspars is present in all samples mineral assemblages in veins include quartz hematite hematite coffinite fluorite quartz and clay minerals minor chlorite and sericite are found in all vein types all granite types are anomalously rich in u concentrations between 10 and 81 ppm highly variable th u ratios as well as hydrothermal u minerals mostly coffinite in granites and veins are clear evidence for u mobility uranium may have been preconcentrated in veins in the upper parts of the pluton and was subsequently leached after deposition of the sediment