trends in river flow affecting the northeastern reach of the san francisco bay estuary over the past 7000 years abstract a variety of stratigraphic analyses particle grain size iron concentration loss on ignition and macrofossils from sediments obtained from two marsh sites are used to reconstruct a middle to late holocene record of stream flow into san francisco bay browns island a freshwater brackish site is located at the confluence of the sacramento and san joaquin rivers and is dominated by stands of scirpus americanus peyton hill is a brackish site located near carquinez straits and is dominated by stands of scirpus robustus twenty five ams 14c dates provide chronostratigraphic control during the holocene discharge from the sacramento and san joaquin rivers was broadly comparable to modern flows however an extended period of higher flow began 3800 cal yr b p and continued for almost two millennia at this time browns island supported phragmites communis a freshwater species and peyton hill supported s americanus at least two floods recognized by discrete increases in sand and silt occurred at 3600 and 530 cal yr b p

the geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the sacramento san joaquin delta california usa a multi proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the sacramento san joaquin delta california three long cores were collected from the mccormack williamson tract mwt and these cores were analyzed for bulk density loss on ignition ne clay and silt content al concentration magnetic susceptibility pollen and charcoal radiocarbon dates obtained for the cores were converted into calendar years and an age depth model was constructed long term vertical accretion and sedimentation rates were estimated from the age depth model cross core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment percentage ne and loi data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5 5 per cent to the site down core grain size pro les show two hydrological domains in the cores namely millennial ne coarse uctuations superimposed on general up core ning coarse sediment is viewed as channel or near channel overbank deposits whereas ne deposits are considered to be distal overbank ood deposits the coarse ne uctuations are indicative of changing depositional settings as channels migrated laterally across mwt whereas the upward ning trend re ects a combination of self limiting overbank deposition as oodplain elevation increased and decreasing competence as sea level rise reduced ood pulse energy slopes mwt has been cross cut and incised numerous times in the past only to have the channels abandoned and subsequently lled by ne sediment the channels around mwt attained their modern con guration about 4000 years ago mwt likely came under tidal in uence at about 2500 cal bp wetlands have recently developed on mwt but they are inorganic sediment dominated copyright 2004 john wiley sons ltd

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

the contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

carbonate platform evolution in a silurian oceanic island a case study from alaska s alexander terrane abstract silurian limestones exposed in the alexander terrane of alaska are the oldest carbonates of wide distribution in the region and represent the evolution of a shallow marine platform in an island arc setting during waning volcanism and the onset of orogenesis four main stages in carbonate platform development are recognized beginning with calcareous turbidites that accumulated on a volcaniclastic ramp in a slope environment overlying deposits record the formation of a metazoan dominated fringing reef and of backreef sites that were affected by cyclic changes in water depth and sedimentation patterns following the earliest effects of orogenesis and widespread progradation of conglomerates small bioherms and biostromes grew in shallow subtidal settings on the rejuvenated platform co temporaneously a consortium of microbial organisms associated with accessory metazoans principally sphinctozoans created a rimmed carbonate shelf with the construction of stromatolite reefs at the seaward edge of the platform during platform drowning downslope transport from the platform margin resulted in significant accumulations of reefal material as debris flows and slumps along a deep marine slope carbonate sedimentation was terminated within the arc as a result of uplift shoaling and progradation of a clastic wedge during culminating phases of the klakas progeny in the late silurian early devonian this island arc suite is characterized by extraordinarily thick platform and periplatform carbonates sequential evolution of fringing and barrier reefs and patterns of faunal t rnover that differentiate these deposits from coeval carbonates that formed under different tectonic conditions a model for carbonate deposition in island arcs involving high rates of sediment accumulation steep submarine slopes crustal instability and biogeographic isolation contributes new data about carbonate platform development in tectonically active oceanic settings

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

obtaining diagenetic ages from metamorphosed sedimentary rocks u pb dating of unusually coarse xenotime cement in phosphatic sandstone the depositional age of nonfossiliferous metamorphosed sedimentary rocks is commonly bracketed between the age of the youngest detrital mineral and the age of the oldest metamorphic mineral the technique of dating diagenetic xenotime by ion microprobe can provide robust minimum ages for sediment deposition however in most cases xenotime is only a few microns m in size and rarely exceeds 10 m the minimum size for in situ ion microprobe analysis phosphatic sandstone in the greenschist facies mount barren group in southwestern australia contains unusually abundant xenotime occurring as exceptionally coarse 200 m pore filling cement that nucleated on detrital zircon grains the optimum environmental site for the formation of the cement was sand beds within a black shale condensed section analysis of xenotime by sensitive high resolution ion microprobe yields two age populations 1696 7 ma for cement adjacent to detrital zircon grains and 1646 8 ma for outer zones preserved textures show that initial xenotime growth was early diagenetic establishing the ca 1700 ma age as a proxy for the depositional age of the mount barren group the younger age ca 1650 ma is regarded as burial related the xenotime data reduce considerably the previous limits on the age of the succession i e between ca 1850 ma youngest zircon population and ca 1200 ma peak metamorphism the significant achievement of our results is establishing that early diagenetic xenotime retains its physical form and u pb isotopic age despite greenschist facies metamorphism and penetrative deformation

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

quaternary tephrochronology and deposition in the subsurface sacramento san joaquin delta california u s a abstract we document characteristics of tephra including facies and geochemistry from 27 subsurface sites in the sacramento san joaquin delta california to obtain stratigraphic constraints in a complex setting analyzed tephra deposits correlate with 1 an unnamed tephra from the carlotta formation near ferndale california herein informally named the ash of wildcat grade 0 780 ma 2 the rockland ash bed 0 575 ma 3 the loleta ash bed 0 390 ma and 4 middle pleistocene volcanic ash deposits at tulelake california and pringle falls bend and summer lake oregon herein informally named the dacitic ash of hood 0 180 ma all four tephra are derived from cascades volcanic sources the rockland ash bed erupted from the southern cascades and occurs in up to 7 m thick deposits in cores from 40 m subsurface in the sacramento san joaquin delta tephra facies and tephra age constraints suggest rapid tephra deposition within fluvial channel and overbank settings likely related to flood events shortly following volcanic eruption such rapidly deposited tephra are important chronostratigraphic markers that suggest varying sediment accumulation rates in quaternary deposits below the modern sacramento san joaquin delta this study provides the first steps in a subsurface quaternary stratigraphic framework necessary for future hazard assessment

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

zabyat formation semail nappe oman sedimentation on to an emplacing ophiolite the pelagic sediments of the semail ophiolite are depositionally overlain by ophiolite derived sediments of the zabyat formation dominated by matrix supported rudites with subordinate arenites and lutites the detritus was locally derived from the ophiolite in a deep marine environment indicated by both underlying and overlying pelagic carbonates the zabyat rocks are restricted to fault zones in the ophiolite which were active during emplacement they are interpreted as debris shed from the sub vertical fault zones during the initial disruption of the semail ocean floor prior to the final emplacement on to the arabian continental margin this interpretation places constraints on possible mechanisms of ophiolite emplacement

neodymium isotopic composition of cambrian ordovician biogenic apatite in the baltoscandian basin implications for palaeogeographical evolution and patterns of biodiversity biogenic apatite preserved in 148 samples of conodonts and organophosphatic shelled brachiopods from cambrian through ordovician successions of the baltoscandian basin baltica plate preserves a sensitive record of early palaeozoic sea water chemistry interpreted via neodymium isotope ratios consistent e nd t values of 9 6 to 8 3 for lower to middle cambrian samples suggest no significant lateral or temporal variation across the region average upper cambrian values are 7 2 to 7 7 sedimentary analysis suggests that the influence of continental weathering from baltica as a major source of radiogenic nd was negligible ordovician samples show a rise to 5 to 6 in the early arenig early mid llanvirn and late caradoc sea water mixing from the southeast iapetus ocean was a constant factor throughout cambrian ordovician times the rise reflects erosion of obducted volcanic arc complexes along the caledonian margin and probably also relates to pollution of the baltica sector of iapetus from the approaching avalonia plate patterns of evolutionary biodiversity and palaeobiogeographical linkages support the geochemical signatures in interpreting the tectonic history of the region extinction of lingulate brachiopod faunas in the tremadoc followed by subsequent recovery and emergence of benthic assemblages typical of the ordovician evolutionary fauna in the billingen early volkhov regional stages coincide with significant changes in geochemical characteristics of water masses across the baltoscandian basin the early and mid ordovician arenig to llandeilo brachiopod faunas of the north estonian confacies belt are characterized by high endemism and low turnover rates whereas increased immigration resulted in the extinction of a number of local lineages in the late llanvirn from the mid caradoc to mid ashgill when baltica was drifting on a course to collide eventually with avalonia and gradually approach laurentia brachiopod assemblages were characterized by higher turnover rates at the same time they gradually became more cosmopolitan and less influenced by the invasion of new faunas

the asaphid trilobite fauna its rise and fall in baltica abstract the baltica terrane is well known as the asaphus province of the ordovician world being situated in intermediate latitudes and surrounded by fairly wide oceans baltica had a benthic fauna that developed in a relatively endemic direction the most common trilobites were the asaphids the present study discusses how they appeared evolved in various environments around baltoscandia and finally disappeared the total range of the asaphids based on data from 381 species is estimated as extending from the furongian latest cambrian to the end ordovician the remnant cambrian olenid fauna which was adapted to black bituminous shale facies survived into the tremadocian this cambrian fauna includes the first asaphids promegalaspides niobella eoasaphus with a shift to lighter coloured and carbonatic sediments in the middle tremadocian this fauna was replaced by the immigrating ceratopyge fauna the latter contains the first five widely distributed asaphid genera promegalaspides niobe niobella niobina and asaphellus as carbonate sedimentation became more widespread in many areas from the floian onwards the asaphids increased in number and formed a stabilised asaphid fauna during the dapingian in baltoscandia a gradual development of endemism related to facies belts is observed during the darriwilian records of the mud related niobines megistaspis and ptychopyge faunas together with some other benthic macrofaunas are not found beyond the boundary of the kunda aseri regional stages middle darriwilian their disappearance may be due to a catastrophic event in contrast asaphus s l survived this interval drift of baltica towards lower latitudes and fluctuations in sea level influenced the asaphid fauna leading to its gradual collapse by late sandbian time influx of the islotelines during the early katian gave way to a set of illaenimorph species found together with corals that are related to a reefal environment this morph disappears prior to the hirnantian glaciation

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

giant uranium deposits formed from exceptionally uranium rich acidic brines the athabasca basin canada is home to some of the world s largest uranium deposits analysis of preserved ore forming fluids and experimental measurement of uranium solubility in analogous solutions show that the giant deposits could have formed relatively rapidly from extremely uranium rich brines under acidic conditions

mantle fragments in the scandinavian caledonides abstract mantle fragments of ultramafic composition are widespread in the scandinavian caledonides sc lenses and boudins of alpine type peridotites in the scandinavian caledonides represent parts of dismembered ophiolite sequences and fragments of sub continental upper mantle metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope usually caledonian metasediments but in places also precambrian metagranitoids forming the basement cores of the nappes caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope metaperidotites of the external massifs display at least a two stage metamorphic history an early caledonian high pressure high temperature phase related to early crustal stacking and a late caledonian regional metamorphic overprint which produced a regular barrovian type metamorphic pattern of in situ metamorphism metaperidotites from nappes in intermediate positions iapetus ocean ophiolites and ultramafic rocks from island arc environments show strongly diverging histories metaperidotites from internal ophiolites oceanic ophiolites koli lack any evidence of subduction metamorphism are serpentinized to various degrees show abundant primary mantle relic mineralogies and the caledonian metamorphic overprint is low metaperidotites from external island arc ophiolites and other associations seve often show relic high pressure metamorphism related to the finnmarkian phase of the caledonian orogeny the seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late caledonian regional metamorphism alpine type peridotites are absent in the foreland of the baltic shield and in the innermost nappes lofoten the metamorphic characteristics and evolution recorded by the metaperidotites in the scandinavian caledonides allow a general reconstruction of the dynamics of collision belt formation

an empirical oxygen and hydrogen isotope geothermometer for quartz tourmaline and tourmaline water abstract oxygen isotope equilibration temperatures of coexisting quartz muscovite illite chlorite and biotite from a variety of geologic environments have been used in conjunction with the 18o and d values of associated tourmaline to formulate empirical quartz tourmaline and tourmaline water isotope fractionation factors over temperatures from 200 to 600 c the fractionation factors determined using this method are as follows 1 1 1000 in quartz tourmaline 1 0 0 17 10 6 t 2 0 39 0 44 oxygen 2 2 1000 in tourmaline water 27 2 4 4 10 6 t 2 28 1 9 8 hydrogen 350 600 c the isotopic properties of tourmaline are nearly identical to those of muscovite and illite despite the significant differences in their crystal structures similarities in the oxygen and hydrogen isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the al si o and si o bonds however the bo3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18o values of coexisting tourmalines and micas d values of coexisting tourmalines and micas are generally concordant to within 10 chemical compositions indicate that varying fe mg ratios in the tourmalines appear to have only a minor control on their d values there is a discontinuity in the 1000 in tourmaline water values for hydrogen at temperatures between 200 c and 300 c suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point as are some other hydrous minerals

long term accretion rates on tidal salt marshes abstract long term variations in salt marsh accretion rates were estimated using data collected on the marshes of the north norfolk coast england fourteen discrete marsh areas were sampled all lying within a 20 km stretch of coast the age of each marsh had previously been determined using radiocarbon or archival evidence for the date of vegetation inception on each marsh surface marsh ages ranged from 10 years to 2000 years the elevation of each marsh surface was determined in the field using levelling techniques the relationship between age and surface elevation was assumed to be a function of the rate of marsh accretion within this area of coast statistical tests showed this to be a highly significant relationship while the accretion rates calculated from the age height curve agree closely with field measurements on these marshes accretion rates were found to vary from 1 7 cm yr on 10 year old marshes to less than 0 002 cm on marshes older than 500 years the age height relationship describes an asymptotic curve with the asymptote lying 0 8 m below the level of the highest spring tides and appears to be controlled by the frequency of tidal maxima which peaks at 0 8 m below the maximum value and declines sharply above that height

hydrothermal transport and deposition of the rare earth elements by fluorine bearing aqueous liquids new technologies particularly those designed to address environmental concerns have created a great demand for the rare earth elements ree and focused considerable attention on the processes by which they are concentrated to economically exploitable levels in the earth s crust there is widespread agreement that hydrothermal fluids played an important role in the formation of the world s largest economic ree deposit i e bayan obo china until recently many researchers have assumed that hydrothermal transport of the ree in fluorine bearing ore forming systems occurs mainly due to the formation of ree fluoride complexes consequently hydrothermal models for ree concentration have commonly involved depositional mechanisms based on saturation of the fluid with ree minerals due to destabilization of ree fluoride complexes here we demonstrate that these complexes are insignificant in ree transport and that the above models are therefore flawed the strong association of h and f as hf and low solubility of ree f solids greatly limit transport of the ree as fluoride complexes however this limitation does not apply to ree chloride complexes because of this the high concentration of cl in the ore fluids and the relatively high stability of ree chloride complexes the latter can transport appreciable concentrations of ree at low ph the limitation also does not apply to sulphate complexes and in some fluids the concentration of sulphate may be sufficient to transport significant concentrations of ree as sulphate complexes particularly at weakly acidic ph this article proposes new models for hydrothermal ree deposition based on the transport of the ree as chloride and sulphate complexes

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

late holocene δ13c and pollen records of paleosalinity from tidal marshes in the san francisco bay estuary california abstract records of stable carbon isotopes 13c are presented from cores collected from four san francisco bay marshes and used as a proxy for changes in estuary salinity the 13c value of organic marsh sediments are a reflection of the relative proportion of c3 vs c4 plants occupying the surface and can thus be used as a proxy for vegetation change on the marsh surface the four marshes included in this study are located along a natural salinity gradient that exists in the san francisco bay and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity the 13c values complement pollen data from the same marsh sites producing a paleoclimate record for the late holocene period in the san francisco bay estuary the data indicate that there have been periods of higher than average salinity in the bay estuary reduced fresh water inflow including 1600 1300 cal yr b p 1000 800 cal yr b p 300 200 cal yr b p and ca a d 1950 to the present periods of lower than average salinity increased fresh water inflow occurred before 2000 cal yr b p from 1300 to 1200 cal yr b p and ca 150 cal yr b p to a d 1950 a comparison of the timing of these events with records from the california coast watershed and beyond the larger drainage of the bay reveals that the paleosalinity variations reflected regional precipitation

stable isotope record of late holocene salinity and river discharge in san francisco bay california abstract oxygen and carbon isotopic measurements of fossil mollusks from san francisco bay are used to derive a record of paleosalinity and paleostreamflow for the past 5 900 years the 18 o and 13 c values of river water 12 and 9 are markedly different than seawater 0 and 1 and vary systematically as a function of salinity in the estuary the data show that annually averaged salinity in the south central part of the bay was very close to the modern diversion corrected value of 26 8 over the past 2 700 years and 4 lower than modern between 3 800 and 5 100 yr b p based on those salinities the average annual river inflow to san francisco bay is calculated to have been 1290 m 3 s over the past 2 400 years and 1990 m 3 s between 3 800 and 5 100 yr b p 1 8 times greater than the modern diversion corrected value of 1100 m 3 s assuming a constant bay volume the inferred river discharge record generally corroborates independent paleohydrologic records in california including tree ring treeline and lake level records

pre and post missoula flood geomorphology of the pre holocene ancestral columbia river valley in the portland forearc basin oregon and washington usa abstract geomorphic landscape development in the pre holocene ancestral columbia river valley 1 5 km width in the portland forearc basin 50 km length is established from depositional sequences which pre date and post date the glacial lake missoula floods the sequences are observed from selected borehole logs 150 in number and intact terrace soil profiles 56 in number in backhoe trenches four sequences are widespread including 1 a vertically aggraded pleistocene alluvial plain 2 a steep sided valley that is incised 125 150 m into the pleistocene gravel plain 3 missoula flood terraces 19 13 ka abandoned on the sides of the ancestral valley and 4 holocene flooding surfaces 11 8 ka buried at 70 30 m depth in the axial columbia river valley weathering rims and cementation are used for relative dating of incised pleistocene gravel units soil development on the abandoned missoula flood terraces is directly related to terrace deposit lithology including thin bw horizons in gravel irregular podzols in sand and multiple bw horizons in thicker loess capping layers radiocarbon dating of sand and mud alluvium in the submerged axial valley ties holocene flooding surfaces to a local sea level curve and establishes holocene sedimentation rates of 1 5 cm year 1 during 11 9 ka and 0 3 cm year 1 during 9 0 ka the sequences of pleistocene gravel aggradation river valley incision cataclysmic missoula flooding and holocene submergence yield complex geomorphic landscapes in the ancestral lower columbia river valley

a 2000 yr record of sacramento san joaquin river inflow to san francisco bay estuary california oxygen and carbon isotopic measurements of fossil bivalves macoma naarfa contained in estuarine sediment are used to reconstruct a late llolocene record of sitlinity and stream flow in san francisco bay discharge into the bay is a particularly good indicator of paleoclin ate in california because the bay s influent streams drain 40 of the state the isotopic record suggests that hetween al oul 1670 ant1 1900 calcnd r yc trs yr cal 1i i inflow to the bay was sul stantially greirler tlian the cstinli tecl precliversion inllow ol 1100 m3 s an unconforn ity representing a 900 yr hiatus is present in the core between 1670 ancl 750 yr cirl ii 13 possil ly r lusc cl by i n tjor 11ydrologic rl event over the p ist 750 yr strcitn ilow to s iii i ril cisco ikty ii is vitrirtl wit11 i pcriotl ol 200 yr i1lter11itte wet iltttl tlry i tlrougl t intc r rls typiritlly 11 rvc i lstecl 40 to 100 yr

tidal wetland record of holocene sea level movements and climate history abstract paleontological geochemical and lithological indicators of former marine and nonmarine influence are correlated between 13 cores from a tidal wetland wolfe glade on the southeast coast of delaware bay twenty new radiocarbon dates are used to establish the chronostratigraphy of marsh facies sediment iron content weight loss on ignition and remains of plants diatoms and foraminifera known to tolerate specific tidal inundation cycles are used to describe cored facies originating from supratidal intertidal and subtidal salt marsh subenvironments pollen assemblages are used to infer local holocene climate fluctuations and to reconstruct paleoenvironments during marsh evolution the record of paleoclimatology suggests the atlantic chron was warm with variable humidity in the region whereas the subboreal was dominated by cool and humid conditions the subatlantic was warmer and initially dryer with a cool humid phase prior to about 1 ka returning to warmer humid conditions in the last several centuries local relative sea level movements are characterized by five rapid short term episodes when the rate of sea level rise accelerated relative to the rate of marsh aggradation these episodes are recorded by transgressive facies contacts at 5 3 0 2 ka 4 4 0 2 ka 3 25 0 2 ka and 1 8 0 2 ka sidereal years an earlier transgressive facies contact dated 6 9 0 2 ka is probably not the product of a true sea level movement sea level movements are recorded throughout the marsh as palustrine or high marsh peats or peaty overlain by lower intertidal or subtidal marine deposits several features suggest that these episodes are local relative transgressions produced by short term accelerations in the rate of sea level rise relative to marsh aggradation the contemporaneity and apparent suddenness of marine inundations the sequence of facies indicating marine drowning the presence of similar events in marshes elsewhere in delaware bay and the marsh wide extent of indicative facies transitions we propose that the rapid and frequent sea level movements observed in wolfe glade are the result of surges and relaxations in the gulf stream and associated spin up and partial collapse of the north atlantic gyre in response to winds generated by changes in the north atlantic atmospheric thermal gradient associated with holocene climate fluctuations

ordovician faunas island arcs and ophiolites in the scandinavian caledonides ordovician faunal data from the scandinavian caledonides is tested with new geochemical information from zircons to give u pb ages and source origins of volcanic arc and ophiolite sequences early ordovician arenig llanvirn low latitude toquima table head faunas from the upper upper allochthon are associated with an island arc system formed adjacent to laurentia contemporaneous mafic magmas were contaminated by crustal material during subduction and associated granites contain inherited zircons of archaean age the nearest source for such rocks is on the laurentian rather than the baltic side higher latitude celtic province faunas from the upper upper allochthon are from one insular site accessible to forms from both laurentia and baltica the late ordovician low latitude holorhynchus and subtropical hirnantia faunas occur in overstep sequences above deeply eroded early ordovician arc complexes the transgression appears to be coeval with a second generation of spreading related complexes single detrital zircons from sediments show sources from archaean proterozoic and early ordovician terranes this suggests that deposition was in a basin situated along the same continental margin laurentia to which the early ordovician ophiolite arc sequences had already become accreted the late ordovician faunas link both laurentia and baltica at a time of narrowing of lapetus the new geochemical data together with the faunal information is supported by recent palaeomagnetic studies

geochemical isotopic and geochronlologic constraints on the formation of the eagle point basement hosted uranium deposit athabasca basin saskatchewan canada and recent remobilization of primary uraninite in secondary structures the athabasca basin hosts many world class unconformity related uranium deposits recently uranium reserves for the eagle point basement hosted deposit have increased with the discovery of new mineralized zones within secondary structures a paragenetic study of eagle point reveals the presence of three temporally distinct alteration stages a pre athabasca alteration a main alteration and mineralization comprised of three substages and a post main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures the pre athabasca alteration stage consists of minor amounts of clinochlore followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and k feldspar caused by surface weathering the main alteration and uranium mineralization stage is related to three temporally distinct substages all of which were produced by isotopically similar fluids a major early alteration substage characterized by muscovite alteration and by precipitation ca sr lree rich aluminum phosphate sulfate minerals both from basinal fluids at temperatures around 240 c prior to 1 600 ma the mineralization substage involved uraninite and hematite precipitated in primary structures the late alteration substage consists of dravite uranophane beta veins calcite veins and sudoite alteration from mg ca rich chemically modified basinal fluids with temperatures around 180 c the post main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca 535 ma u pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb to a distance of at least 225 m above the mineralized zones

topographic features of the sub athabasca group unconformity surface in the southeastern athabasca basin and their relationship to uranium ore deposits topographic features of the sub athabasca unconformity surface such as paleovalleys topographic highs and fault scarps have been documented locally in the eastern athabasca basin and available data indicate that they are spatially associated with mineralization however the mechanisms by which such topographic features were generated their size and distribution at the regional scale as well as their relationship to mineralization are still not completely understood a 100 by 60 square kilometre area of the southeastern athabasca basin encompassing the mcarthur river phoenix and key lake deposits was selected to study the relationship between these topographic features and u mineralization in this region three dominant sets of sub vertical faults were identified on the basis of aeromagnetic data northeast trending north northwest trending and northwest trending a detailed three dimensional 3 d model of this part of the basin was constructed using data from more than 1200 drill holes th

a 4300 year strontium isotope record of estuarine paleosalinity in san francisco bay california abstract strontium isotopic compositions of carbonate mollusk shells from estuarine sediments cored beneath san francisco bay are used to derive a record of mean annual salinity and average freshwater inflow to the estuary for intervals during the past 4300 yrs the large difference in the 87sr 86sr ratio between seawater 0 7092 and the average freshwater entering the estuary 0 7065 produces a correlation between 87sr 86sr and salinity in bay waters that can be detected with high precision measurements paleosalinity is inferred from the 87sr 86sr ratio measured in fossil carbonate shells of bivalves preserved in the sediment because salinity in san francisco bay is primarily controlled by the freshwater inflow from the sacramento and san joaquin rivers the paleosalinity record can be converted to a paleodischarge record using a transfer function derived from historical data salinity data are referenced to modern values estimated for the estuary after correcting for the lower discharge caused by diversion since 1850 a d data are presented from richardson bay located near the estuary mouth modern mear arrival salinity mas of ca 24 and from san pablo bay located about 30 km upstream modern mas of ca 18 20 for richardson bay the data cover the periods 0 600 yrs b p and 2200 4300 yrs b p based on radiocarbon dating for san pablo bay the periods 0 130 yrs b p and 2500 2800 yrs b p are represented the richardson bay data indicate extended periods of low salinity relative to modern indicating higher freshwater inflow at ca 80 220 310 440 500 3100 3400 and 4300 yrs ago the data indicate high salinity relative to modern hence lower freshwater inflow at about 40 140 210 270 2100 and 3450 3700 yrs b p for san pablo bay where salinity resolution is better salinity was lower than modern during the period at ca 50 and 2550 2650 yrs b p and higher than modern at ca 90 110 155 and 2510 2530 yrs b p the data suggest that mean annual discharge to san francisco bay typically varies between values that are below the modern value 600 m3 s and values 2 to 3 times as high the average paleosalinity is typically substantially lower than the modern values the 4300 yr average freshwater inflow is estimated to be 1200 200 m3 s the record indicates that quasi cyclic variations in mean annual discharge occur naturally with a period of about 200 yrs or less

234u 238u and δ87sr in peat as tracers of paleosalinity in the sacramento san joaquin delta of california usa abstract the purpose of this study was to determine the history of paleosalinity over the past 6000 years in the sacramento san joaquin delta the delta which is the innermost part of the san francisco estuary we used a combination of sr and u concentrations 87sr values and 234u 238u activity ratios ar in peat as proxies for tracking paleosalinity peat cores were collected in marshes on browns island franks wetland and bacon channel island in the delta cores were dated using 137cs the onset of pb and hg contamination from hydraulic gold mining and 14c a proof of concept study showed that the dominant emergent macrophyte and major component of peat in the delta schoenoplectus spp incorporates sr and u and that the isotopic composition of these elements tracks the ambient water salinity across the estuary concentrations and isotopic compositions of sr and u in the three main water sources contributing to the delta seawater sacramento river water and san joaquin river water were used to construct a three end member mixing model delta paleosalinity was determined by examining variations in the distribution of peat samples through time within the area delineated by the mixing model the delta has long been considered a tidal freshwater marsh region but only peat samples from franks wetland and bacon channel island have shown a consistently fresh signal

experimental diffusion of hydrogen into synthetic fluid inclusions in quartz quartz hosted synthetic co2 h2o fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory simulated metamorphic re equilibration at 650 750 and 825 c and 1 5 kbar total pressure with fo2 defined by the c ch4 buffer microthermometry and raman spectroscopy show that the initial co2 h2o inclusions become co2 ch4 h2 h2o inclusions after diffusive influx of hydrogen from the reducing confining medium measurable changes are observed in inclusion compositions after only 15 days of re equilibration implying significant hydrogen mobility at still lower temperatures over geological time spans results of synthetic inclusion re equilibrium experiments have profound implications for the interpretation of natural fluid inclusion data failure to account for potential hydrogen migration in inclusions from high temperature geological environments may lead to erroneous estimates of p t and or the compositions of metamorphic fluids

improved calibration procedures and new standards for u pb and th pb dating of phanerozoic xenotime by ion microprobe abstract xenotime is a widely occurring mineral that is amenable to u pb and th pb dating but often is found as micrometre sized crystals that can only be dated by in situ microanalytical techniques determining accurate ages for phanerozoic samples and assessing concordance in older samples requires accurate determination of pb u and pb th however ion microprobe data for these ratios are affected by the highly variable trace element composition of xenotime we have identified calibration procedures including matrix corrections for the effects of the dominant trace elements u th and ree that provide an accuracy of 1 for pb u and

the relationships between late ordovician sea level changes and faunal turnover in western baltica geochemical evidence of oxic and dysoxic bottom water conditions abstract the late sandbian to the early katian late ordovician in southeastern norway is dominated by marine mudstones that contain an exceptional spectrum of macrofauna and trace element geochemistry recording both abrupt and gradual faunal changes during major sea level and environmental shifts this study investigates the relationships between sea level changes and their influence on the source of clastic material oxygen levels in the bottom water and faunal changes with special emphasis on the brachiopod fauna trace element ratios indicate that nearly stable upper dysoxic bottom water conditions prevailed in the northwestern part of the baltoscandian sea the exception is during the major shallowing in the earliest katian when there was an abrupt shift to oxic conditions as the sea bottom came within a normal storm wave base nonetheless the pre shallowing epibenthic fauna though not the shelly endobenthic in this area was rich and diverse and two major immigration phases of new brachiopod taxa are seen well before the shallowing this indicates that the immigration of new taxa was not the result of an increase in oxygen content in the bottom water more brachiopod genera stayed during the abrupt shallowing and increased oxic level than did during the following gradual return to deeper dysoxic environments the major brachiopod immigration phases took place markedly earlier in this northwestern part of the baltoscandian sea than in the central part eastern baltic and possibly also the comparable faunal turnover in laurentia the following disappearance of taxa during an early katian transgressive event coincided with the faunal turnover in the shallow water environments of the east baltic the depositional history was consistent within the investigated mudstone dominated offshore facies of the oslo region which are comparable to the central baltoscandian confacies belt of baltoscandia the composition of the siliciclastic material which was deposited in the basin was nearly constant through the sequence though the land area expanded to include ophiolites expressed by cr enrichment coinciding with the major sea level drop the cr enrichment indicates that by that time at least the ophiolite complexes north of the oslo region became subaerially exposed this enrichment thus forms a potential geochemical marker horizon representing the basal katian stage

discordant 14c ages from buried tidal marsh soils in the cascadia subduction zone southern oregon coast peaty tidal marsh soils interbedded with estuarine mud in late holocene stratigraphic sequences near coos bay oregon may have been submerged and buried during great m 8 subduction earthquakes smaller localized earthquakes or by nontectonic processes radiocarbon dating might help distinguish among these alternatives by showing that soils at different sites were submerged at different times along this part of the cascadia subduction zone but comparison of conventional 14c ages for different materials from the same buried soils shows that they contain materials that differ in age by many hundreds of years errors in calibrated soil ages represent about the same length of time as recurrence times for submergence events 150 500 yr this similarity precludes using conventional 14c ages to distinguish buried soils along the southern oregon coast accelerator mass spectrometer 14c ages of carefully selected macrofossils from the tops of peaty soils should provide more precise estimates of the times of submergence events

shrimp u pb ages of diagenetic and hydrothermal xenotime from the archaean witwatersrand supergroup of south africa shrimp dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition thus xenotime dating has significant economic application to precambrian sediment hosted ore deposits such as witwatersrand au u for which there are no precise depositional ages the growth history of xenotime in the witwatersrand supergroup is texturally complex with several phases evident the oldest authigenic xenotime 207pb 206pb age obtained in sandstone underlying the vaal reef is 2764 5 myr 1 and most likely represents a mixture of diagenetic and hydrothermal growth nevertheless this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition other xenotime data record a spread of ages that correspond to numerous post diagenetic thermotectonic events including a ventersdorp event at 2720 ma up to the 2020 ma vredefort event

hydrothermal dolomite a product of poor definition and imagination abstract the latest dolomite bandwagon is the hydrothermal dolomite model in its present form this bandwagon is doomed or at least very much overstated for at least two reasons 1 there are several definitions of hydrothermal and hardly any author specifies which one s he is using 2 very few of the dolomites hitherto called hydrothermal have been demonstrated to be hydrothermal according to any definition except the worst as presently applied the term hydrothermal dolomite is confusing and or meaningless we suggest to use white s geol soc amer bull 68 1957 1637 time honored definition of hydrothermal as aqueous solutions that are warm or hot relative to its surrounding environment with no genetic implications regarding the fluid source hence a dolomite should be called hydrothermal only if it can be demonstrated to have formed at a higher than ambient temperature regardless of fluid source or drive furthermore this definition does not carry a lower or upper temperature limit even a dolomite formed at 40 c could be hydrothermal by extension dolomites formed at temperatures lower than ambient are not hydrothermal even if they formed at a rather high temperature for example groundwater may penetrate a rock sequence through a highly permeable pathway such that it is heated to 150 c at a depth where the surrounding rock has a temperature of 250 c we suggest to call dolomite formed from this water hydrofrigid dolomite formed in or near thermal equilibrium with the surrounding rocks may be called geothermal furthermore not all saddle dolomite formation requires advection fluid flow to transport mg saddle dolomite can be formed in at least three ways i e from advection local redistribution of older dolomite during stylolitization and as a by product of thermochemical sulfate reduction in a closed or semi closed system only the first and the last of these three possibilities have a chance of being hydrothermal almost all dolomites and dolostones in the western canada sedimentary basin have recently been re interpreted as hydrothermal applying the rationale outlined above reveals however that this basin contains very little hydrothermal dolomite rather most dolomites in this basin and almost all dolostones south of the peace river arch are geothermal and or the proof of a hydrothermal origin has not been made this has important implications beyond the various case studies at hand as attempts to tie dolomitization to orogenic events become moot at least in the southern part of the basin

the paleoecology and stratigraphy of nichols meadow sierra national forest california usa sediment stratigraphy and pollen plant macrofossil and charcoal analyses along with nine radiocarbon dates from nichols meadow provides the most intensive investigation of sierra nevada montane meadow development and paleoecology during pollen zone nm i ca 18 500 12 500 yr b p the nichols meadow area contained a stream during the tioga glacial stage the presence of high artemisia and gramineae pollen percentages along with a very low pollen influx rate reflects a cold dry steppe woodland environment pollen zone nm ii ca 12 500 8800 yr b p documents the development of a lower montane forest and giant sequoia sequoiadendron giganteum community which existed around a small meadow the higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments arly holocene aridity is recorded in pollen zone nm iii ca 8800 6000 yr b p by poorly preserved pollen we infer that the forest trees closed in on the meadow and occupied the meadow floor the reduction in available moisture caused giant sequoia to become locally extinct in the nichols meadow area probably moving into their current distribution within the nelder grove pollen zone nm iv 6000 yr b p present reflects the development of the modern nichols meadow less sand in the meadow sediments due to stable vegetation surrounding nichols meadow allowed the increased retention of ground water this along with the neoglacial cooling trend at ca 3000 yr b p caused ground water to rise and saturate the meadow these events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate overgrazing and channeling of the meadow s outflowing stream caused the water table to drop resulting in the incision of the meadow

geochemical modeling of the formation of an unconformity type uranium deposit petrologic studies of alteration associated with uranium mineralization in unconformity type uranium deposits have established a detailed paragenetic sequence of the preore and synore alteration in addition fluid inclusion studies have determined the presence of two distinct fluids and thermodynamic analysis of the alteration assemblages has defined their basic characteristics these fluids were probably basinal brines derived from the overlying sandstones and have been distinguished by their different salinities fluids responsible for alteration and ore formation were na ca cl brines speciation calculations suggest that the hydrothermal fluids responsible for the formation of unconformity type uranium deposits were distinguished by their high oxygen fugacity and relatively low ph uranium was transported mainly as uranyl chloride complexes reconstruction of the reactions associated with the formation of the deposits employing chemical mass transfer calculations helps unravel the geochemical processes operating during their genesis reaction path calculations indicate that fe present in aluminosilicates in the host rocks is the principal reductant of oxidized uranium present in the ore forming fluids the use of variable host rock lithologies results in the reproduction of mineralogical features unique to each deposit along with the characteristics common to all unconformity related uranium deposits the calculations show that the observed paragenesis is a function not only of the fluid chemistry but also of the host rock lithologies the modeling indicates that although an orebody can be produced with or without graphite as a reactant its presence leads to a better agreement with the observed alteration paragenesis

holocene paleoclimate records from a large california estuarine system and its watershed region linking watershed climate and bay conditions abstract the san francisco bay delta system includes a watershed that covers a large area of california and provides water to two thirds of the state s population climate over the estuary and its watershed in the dry summer months is controlled by the subtropical high which dominates and deflects storms from california the subtropical high weakens and migrates south as the aleutian low strengthens bringing wet winter storms to the region paleoclimatic records from the bay and its greater watershed spanning the holocene are reviewed here in order to better understand natural variations of precipitation and runoff and the linkages between those variations and the salinity and ecosystems of the estuary to better understand regional scale climate patterns paleoclimate records from coastal california and the great basin are also considered large fluctuations in climate have occurred during the period of interest and there is generally good agreement between the paleoclimate records from different regions early holocene climate throughout california was marked by rising temperatures and reduced moisture as seen in fire records from the watershed this warmth and aridity peaked about 5000 7000 years ago and was followed by a cooling trend with variable moisture conditions the estuary formed relatively rapidly in response to a high rate of sea level rise that dominated the holocene until about 6000 years ago and the subsequent reduced rate of inundation allowed vast tidal marshes to form along the edges of the estuary which have since been recording changes in environmental conditions the impacts of changing regional climate patterns are experienced in the san francisco bay delta system as altered fresh water flows result in altered estuary salinity for example approximately 3800 cal yr b p records from throughout the state indicate a cool moist period and bay salinity was reduced this period was followed by a general drying trend throughout california over the last two millennia punctuated by decades to centuries long droughts and brief extremely wet events in particular during the period ca 1000 800 cal yr b p a d 950 1150 conditions seem to have been unusually dry in many parts of the watershed reducing the fresh water flows to the estuary and shifting tidal marsh plant assemblages toward less diverse but more salt tolerant plants in contrast the little ice age ca 550 200 cal yr b p brought unusually cool and wet conditions to much of the watershed and lowered salinity in the bay many reconstructions suggest that notably stable conditions have prevailed over the instrumental period i e after ca a d 1850 even including the severe short term anomalies experienced during this period interdecadal variability is common in many of the records with timescales of ca 55 70 90 100 150 and 200 years

uraniferous diagenetic xenotime in northern australia and its relationship to unconformity associated uranium mineralisation stratabound uraniferous diagenetic xenotime cements provide a minimum depositional age of 1 632 3 ma for the sedimentary birrindudu group in the killi killi hills tanami region in northern australia the age of xenotime formation is broadly coeval with that recently proposed 1 650 1 600 ma for uranium mineralisation in the unconformity associated deposits of the pine creek inlier northern australia and athabasca basin canada the geological setting and formation model for the uraniferous xenotime crystals are similar to those widely proposed for unconformity associated uranium deposits suggesting a genetic link between the two however xenotime formation in the birrindudu group occurred during an apparently earlier stage of diagenesis compared to late diagenetic formation of unconformity associated uranium deposits this could be explained by variations in the thickness of sediment cover and diachronous diagenesis across the basin at the time of the basin wide uranium mobilisation event herein dated at ca 1 630 ma in such a scenario stratabound uraniferous xenotime cements could represent the remote distal zones of a more deeply buried uranium mineralising system alternatively the xenotime layer represents a precursor to or a source for later unconformity associated ore deposition in this case the presence of diagenetic uraniferous xenotime in an area prospective for unconformity associated uranium mineralisation would be an indication of and still provide an approximate age for uranium mobilisation within the cover sequence xenotime is a far more robust mineral than uraninite for u pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent recrystallisation events if present in the immediate uranium ore environment

the palaeogeography of early ordovician iapetus terranes an integration of faunal and palaeomagnetic constraints abstract new and existing fossil data from ireland britain newfoundland and scandinavia emphasize a significant degree of latitudinal variation in biogeographic patterns across the ordovician iapetus ocean platform provinces together with marginal belts and island complexes can be recognised with increasing clarity on the basis of palaeontological information statistical analysis of the distribution patterns of about 70 early ordovician brachiopod genera across some 25 sites using both cladistic and phenetic methods together with a critical analysis of their geological settings combined with current palaeogeographic and palaeomagnetic data reaffirm the existence of the celtic brachiopod province during the early ordovician the majority of sites assigned to the celtic province define a high latitude peri gondwanan belt shadowing the distribution of the low latitude circum laurentian toquima table head faunas rapidly changing ordovician faunal signals across the baltic province and exploits zone of central newfoundland track the cross latitude movement of these terranes from high temperate to near tropical belts during the period new fossil information together with continuing statistical appraisal of an expanding database are providing more accurate and sophisticated models for the dynamics of the iapetus ocean system

uranium in iron oxide copper gold iocg systems the olympic dam iron oxide copper gold iocg deposit is currently the world s largest producer of uranium other iocg deposits generally have anomalous though uneconomic uranium grades the fluids that generate iocg deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium the reasons for uranium enrichment in certain iocg deposits remain speculative but could include the composition of mineralization related magmas of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization there is sparse data available on uranium abundance in iocg ores there is even less reliable data on the uranium content of unaltered wall rocks for the deposits however the data that is available suggest that the uranium grade of iocg deposits may be primarily related to the uranium content of their unaltered host rocks many iocg deposits appear to have approximately 10 to 40 times enrichment in the ore compared to unaltered host rocks this suggests that exploration for uranium rich iocg deposits should focus on areas with anomalously high uranium contents in host rock sequences

contact relationships in the southeastern trondheim nappe complex central southern norway implications for early paleozoic tectonism in the scandinavian caledonides abstract the upper allochthon a composite thrust complex containing elements of an accreted terrane has long been a controversial feature in the scandinavian caledonides although final emplacement of the upper allochthon occurred during the siluro devonian scandian orogeny the complex experienced an intricate and still debatable early paleozoic history in the central norwegian caledonides the upper allochthon comprises the trondheim nappe complex which contains an enigmatic axial unit of metasedimentary and meta igneous rocks flanked by oceanic crustal sequences to the east and west determination of the nature of internal contacts and timing of assembly of the trondheim nappe complex has been hampered by wide variations in lithology strain and metamorphic grade and scanty age constraints in some rock units in the lake savalen area southeastern trondheim nappe complex a polydeformed continental margin quartzite schist sequence occurs in the core of the einunnfjellet dome these rocks which can be linked to the baltoscandian miogeocline were overthrust by oceanic crust and pelagic sediment then eroded and unconformably succeeded by polymict conglomerates and fine grained clastic sediments early thrust and unconformable contacts were later overprinted by scandian deformation and metamorphism the garnet isograd cuts across lithologie contacts and does not appear to be folded or interrupted by faulting within the 250 km 2 map area regional correlations indicate the widespread occurrence of tectonostratigraphic relationships similar to the einunnfjellet savalen area and imply that prior to the scandian orogeny portions of the upper allochthon were assembled into a composite mass consisting of 1 1 a lower baltoscandian miogeoclinal sequence 2 2 a thrust complex of fragmented oceanic terranes 3 3 an unconformable succession that overstepped both 1 and 2 this mass was subsequently thrust eastward imbricated and metamorphosed during scandian orogenesis as a result of the pervasive scandian overprint pre scandian faults and unconformable contacts in the upper allochthon are commonly cryptic

island arc elements and arc related ophiolites abstract all major structural elements in island arc systems fore arc magmatic arc back arc basins and remnant arcs are potential ophiolite sources and those features that allegedly characterise ophiolites of ocean ridge origin sheeted dyke complexes mantling pelagic rocks hydrothermal metamorphism and associated mineralization can also arise within arc settings age relations are critical in the interpretation of arc related ophiolites remnants of oceanic lithosphere identified by a pre arc initiation age are restricted to fore arc magmatic arc and remnant arc elements as are ophiolite masses generated at the inception of underthrusting the latter apparently common in ancient fore arc terrains form in nascent arc systems in which the rate of role back of the subduction hinge exceeds the rate of convergence spreading occurs above a foundering slab resulting in some arc like compositional features in simple arc systems later ophiolitic rocks have formed either in the active back arc basin or the magmatic arc only those ophiolites that have resided within or very close behind magmatic arcs should show calcalkaline or arc tholeiite magmatic affinities or be intruded or overlain by these rocks volcanic derived sediment or pelagic material may mantle ophiolites from all arc settings but pelagic rocks will generally dominate in stratigraphic sequences above remnant arcs and on back arc basin floors except adjacent to the magmatic arc ophiolites generated at major ocean ridges are unlikely to be immediately overlain by sediment with a significant volcanic component whereas such detritus may lie directly on arc inception arc and back arc ophiolites some arc derived ophiolites are preserved in their original tectonic position others can be identified from their internal features their relationship to other tectonic elements and the nature of associated rocks

spring climate and salinity in the san francisco bay estuary salinity in the san francisco bay estuary almost always experiences its yearly maximum during late summer but climate variability produces marked interannual variations the atmospheric circulation pattern impacts the estuary primarily through variations of runoff from rainfall and snowmelt from the sierra nevada and secondarily through variations in the near surface salinity in the coastal ocean while winter precipitation is the primary influence upon salinity in the estuary spring climate variations also contribute importantly to salinity fluctuations spring atmospheric circulation influences both the magnitude and the timing of freshwater flows through anomalies of precipitation and temperature to help discriminate between the effects of these two influences the record is divided into subsets according to whether spring conditions in the region are cool and wet warm and wet cool and dry or warm and dry warm springs promote early snowmelt driven flows and cool springs result in delayed flows in addition to effects of winter and spring climate variability operating on the watershed there are more subtle effects that are transmitted into the estuary from the coastal ocean these influences are most pronounced in cool and dry springs with high surface salinity ss in the coastal ocean versus cool and wet springs with low ss in the coastal ocean a transect of ss records at stations from the mouth to the head of the bay suggests that the coastal ocean anomaly signal is attenuated from the mouth to the interior of the estuary in contrast a delayed postsummer signal caused by winter and spring runoff variations from the upstream watershed are most pronounced at the head of the estuary and attenuate toward the mouth

discrimination of estuarine marsh subenvironments san francisco bay california u s a using a multivariate statistical calibration of abiotic sediment properties abstract multivariate analysis of a suite of sediment characteristics provides a novel inexpensive and time efficient approach to characterizing estuarine depositional subenvironments especially in the absence of diagnostic microfossils and macrofossils the development calibration and implementation of a statistical model are discussed using data collected from the san francisco bay estuary california forty seven surface sediment samples were collected from three marshes within the san francisco bay estuary and from six different subenvironments ranging from tidal salt marsh below mean higher high water mhhw to tidal freshwater marsh sediments located above mhhw sediment samples were analyzed for percent organic content percent water content percent clay content sediment density and iron concentration standard statistical analysis of the data indicates that changes in sediment characteristics exist within and between the individual marshes however individually these characteristics are insufficient to distinguish among marshes and subenvironments multivariate analysis therefore is employed to consider the array of sediment characteristics simultaneously the individual marsh research sites are treated as idealized reference types the results indicate a strong degree of and statistically significant predictive capability these surface data and analyses are used in the interpretation of stratigraphic cores from three sites in san francisco bay the results using this method were broadly consistent with interpretations using traditional methods however this method determined more subtle variability than was previously recognized

matrix effects and calibration limitations in ion probe u pb and th pb dating of monazite abstract monazite can be used for u pb and th pb dating of a wide variety of rocks and geological processes particularly metamorphism in many instances ion microprobe analysis is the preferred method for dating monazite combining good analytical precision with m scale spatial resolution however ion microprobe dates can be compromised by matrix effects on the ionisation efficiencies of different secondary ionic species which can bias monazite pb tho n and pb uo n data by as much as 40 and 30 respectively for known monazite compositions these effects appear to be entirely attributable to the sputtering process in which case similar effects exist in data from all ion probes the effects on data ratios are modified sometimes exacerbated or reversed when data are subjected to the correlation based pb th and pb u calibrations that are now commonly used one dimensional calibrations of 206 pb 270 uo 2 and 208 pb 264 tho 2 are recommended corrections derived from data for a suite of reference materials with diverse compositions can reduce biases in 208 pb 232 th ages to 206 pb 238 u ages to 204 pb can be addressed without iterative data reduction

origin of uranium deposits revealed by their rare earth element signature uranium deposits form in a wide range of geological settings including deep magmatic to surficial conditions and range in age from archaean to recent these temporal and spatial variations have given rise to an extreme diversity of ore deposits however understanding their conditions of formation has remained challenging this article reports rare earth element ree abundances measured by microbeam methods in uranium oxides for a series of worldwide uranium occurrences the ree patterns are very specific to each deposit type and directly reflect the conditions of their genesis we propose an evaluation of the first order parameters controlling the ree behaviour in each mineralised system this study demonstrates that the ree pattern is the most efficient tool for constraining the geological models of uranium deposits and for genetically discriminating new uranium discoveries this approach may form the starting point for a new procedure in the fight against nuclear trafficking

textural and geochemical discrimination between xenotime of different origin in the archaean witwatersrand basin south africa abstract xenotime ypo4 of detrital diagenetic and hydrothermal origin within siliciclastic rocks of the archaean witwatersrand basin south africa has been identified on the basis of petrography and in situ ion microprobe shrimp age data the chemical composition of xenotime determined by in situ electron microprobe analysis can be correlated with its origin this allows the origin of any xenotime grain to be assessed by a non destructive microanalytical method prior to ion microprobe geochronology the main chemical discriminators are mree hree abundance normalised hree slope and eu anomaly and in some cases u and th contents igneous detrital xenotime 2800 ma is distinguished from diagenetic 2780 ma and hydrothermal

llanvirnian ord iron ooids in baltoscandia element mobility ree distribution patterns and origin of the ree abstract the chemical and mineralogical compositions of llanvimian ordovician iron and associated phosphate ooids from sweden estonia and russia have been examined the oolites are generally thin and lean mud supported and dominated by fe oxyhydroxide goethite limonite ooids one swedish oolite contains a mixture of chamosite goethite and hematite ooids and it is suggested that the two latter types were derived from chamosite ooids by early diagenetic alteration the ree distribution patterns were unaffected by these reactions all ooids in the area show a typical negative eu anomaly inherited from the source material major and minor element contents in limonite and chamosite ooids are similar whereas their ree patterns are different limonite ooids have a lree hree ratio from 1 to 2 4 and chamosite ooids from 3 to 5 the amounts of ree in the ooids are strongly dependent on the amount of phosphate

oxygen isotope seasonality in a temperate estuarine shell midden a case study from ca ala 17 on the san francisco bay california abstract seasonality determination using stable oxygen isotope 18 o analyses in archaeological mollusk shell has been largely limited to aquatic settings where one of the two factors that control shell 18 o water 18 o or salinity and temperature is assumed to be constant open coastal marine environments reflect the former situation and tropical estuaries constitute the latter in an effort to expand stable isotope seasonality to an ecological setting where neither variable remains constant we present a model of annual shell 18 o cycle of aragonite deposition derived from instrumental data on salinity and temperature from san francisco bay california the predicted range of modeled shell 18 o is consistent with observed 18 o values in prehistoric and modern shells when local conditions are considered measurements of 18 o taken at 0 mm and 2 mm from the terminal growth margin were made on 36 archaeological specimens of macoma nasuta from a late holocene hunter gatherer site ca ala 17 and season of collection was inferred using the shell 18 o model we conclude that shellfish exploitation occurred through the year with the exception of fall which may indicate scheduling conflicts with acorn harvesting or other seasonally abundant resources elsewhere the model supports the feasibility of stable isotope seasonality studies in temperate estuaries provided that instrumental records are available to quantify the relevant water conditions at appropriate spatial and temporal scales

palaeoclimatic and archaeological evidence for a 200 yr recurrence of floods and droughts linking california mesoamerica and south america over the past 2000 years conspicuous grey clay rich flood deposits in the predominantly olive varved sediment in the central santa barbara basin california were dated via varve counting to c ad 212 440 603 1029 1418 and 1605 the 200 yr quasi periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented 200 yr periodicity in palaeoclimate records elsewhere the floods of c ad 440 and ad 1418 occurred during global reorganizations of atmospheric circulation cold spells seem to have accompanied the floods of c ad 1029 and ad 1605 california floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a 200 yr periodicity our compilation of palaeoclimatic and mesoamerican and south american archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in 200 yr steps the matching patte

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

a large california flood and correlative global climatic events 400 years ago a gray silt layer 1 2 cm thick in the central santa barbara basin dated by varve counts to a d 1605 5 yr implies an intensity of precipitation flooding of regional rivers and transport of terrigenous detritus unmatched in the last 1000 yr the inferred flood may correlate with the reported rare occurrence of a perennial lake 14c dated to 390 90 b p in california s mojave desert 300 km east of the area draining into the santa barbara basin the dating of the a d 1605 5 yr flood event is consistent with tree ring evidence for a wet and cold paleoclimate elsewhere in the region regional and global climate evidence indicates that much of the world also experienced rapid intense cooling around a d 1605 this cooling was probably accompanied by an equatorward shift of prevailing wind patterns and associated storm tracks

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record

palynologic and geomorphic evidence for environmental change during the pleistocene holocene transition at point reyes peninsula central coastal california abstract three sites on the point reyes peninsula california provide evidence of major environmental change during the pleistocene holocene transition a 12 300 yr long pollen record from coast trail pond reveals a change from closed canopy pseudotsuga abies forest to coastal scrub and grassland about 10 000 yr b p the same change is also evident in pollen records from two sea cliff exposures that contain a series of buried soils interstratified with fluvial and debris flow deposits eight radiocarbon dates from these exposures indicate that aggradation at both sites began ca 12 000 yr b p and that the change from forest to scrub and grassland occurred between 10 300 and 9400 yr b p high percentages of alder pollen and bracken fern spores reflect repeated geomorphic disturbance at ca 10 400 yr b p the occurrence of major aggradation accompanied by recurrent debris flows between ca 12 000 and 10 000 yr b p suggests that this was a period of more frequent high intensity storms