early hydrothermal carbon uptake by the upper oceanic crust insight from in situ u pb dating it is widely thought that continental chemical weathering provides the key feedback that prevents large fluctuations in atmospheric co2 and hence surface temperature on geological time scales however low temperature alteration of the upper oceanic crust in off axis hydrothermal systems provides an alternative feedback mechanism testing the latter hypothesis requires understanding the timing of carbonate mineral formation within the oceanic crust here we report the first radiometric age determinations for calcite formed in the upper oceanic crust in eight locations globally via in situ u pb laser ablation inductively coupled plasma mass spectrometry analysis carbonate formation occurs soon after crustal accretion indicating that changes in global environmental conditions will be recorded in changing alteration characteristics of the upper oceanic crust this adds support to the interpretation that large differences between the hydrothermal carbonate content of late mesozoic and late cenozoic oceanic crust record changes in global environmental conditions in turn this supports a model in which alteration of the upper oceanic crust in off axis hydrothermal systems plays an important role in controlling ocean chemistry and the long term carbon cycle

oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

u pb geochronology of calcite mineralized faults absolute timing of rift related fault events on the northeast atlantic margin constraining the timing of brittle faulting is critical in understanding crustal deformation and fluid flow but many regional scale fault systems lack readily available techniques to provide absolute chronological information calcite mineralization occurs in crustal faults in many geological settings and can be suitable for u pb geochronology this application has remained underutilized because traditional bulk dissolution techniques require uncommonly high u concentration because u and pb are distributed heterogeneously throughout calcite crystals high spatial resolution sampling techniques can target domains with high u and variable u pb ratios here we present a novel application of in situ laser ablation inductively coupled plasma mass spectrometry la icp ms to basaltic fault rock geochronology in the faroe islands northeast atlantic margin faults that are kinematically linked to deformation associated with continental break up were targeted acquired ages for fault events range from mid eocene to mid miocene and are therefore consistently younger than the regional early eocene onset of ocean spreading highlighting protracted brittle deformation within the newly developed continental margin calcite geochronology from la icp ms u pb analysis represents an important and novel method to constrain the absolute timing of fault and fluid flow events

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

vein calcite dating reveals pyrenean orogen as cause of paleogene deformation in southern england an improved method of u pb dating of vein calcite formed during deformation is used to determine the age and cause of folding along the south coast of england fractures arising from folding of late cretaceous chalk of southern england occurred 34 7 1 7 myr ago underlying jurassic strata have veins within fractures with ages of 55 48 42 39 37 34 31 and 25 ma with 34 31 ma being the tectonic culmination folding was slightly younger than the age of the youngest strata in the overlying solent group suggesting that folding terminated basin sedimentation this age of north south shortening is inconsistent with attribution to intraplate forces from the mainly younger alps but is plausibly a result of the pyrenean orogen which evolved from 50 to 28 myr ago with a late eocene culmination a modified method for carbonate laser ablation inductively coupled plasma mass spectrometry u pb dating is presented that uses measured 232 th and 208 pb as a better monitor of common pb and it has distinct advantages over existing methods initial common lead determined on samples conforms closely to model compositions calculated by earlier workers with free regressions giving the most robust dates the modified method is applicable to structural geology carbonate diagenesis and to dating of carbonate relevant to palaeo environmental and archaeological studies supplementary material details of sample locations and characteristics photographs of sample localities microscopic images of veins details of the experimental procedure and u pb data for all samples and reference materials are available at https doi org 10 6084 m9 figshare c 3997086

signature of enso signals in the coral growth rate record of arabian sea and indian monsoons we examine here three sets of recently published data 1 updated indian rainfall irf time series of the entire country covering the time span of 1826 1994 2 coral growth rate time series for a period of 42 years spanning 1948 1990 from the arabian sea and iii nino3 temperature records to investigate the signature of enso response of the indian monsoon multiple spectral techniques e g multi taper method mtm maximum entropy method mem wavelet and cross spectra are used to identify the coherent cyclic and nonstationary modes in these records mtm analysis of irf time series resolves statistically significant variability 90 c i i at multi decadal 66 70 year s scales related to the well known global temperature variability of internal atmospheric ocean origin ii relatively weak signals at 13 and 22 years solar cycles and iii the 2 5 to 7 5 year cycles associated with the enso frequency band the mtm spectra of the coral growth rate record also reveal statistically significant periodicities 90 c i within 1 8 4 2 enso frequency band and a relatively weak signal at 12 8 years mem analysis confirms the stability of above spectral peaks wavelet spectral analyses of the above time series reveal nonstationary localized modes of enso evolution corresponding to 2 7 years and higher order terms although matching periodicities are present in these records cross spectral analysis of irf and nino3 temperature records exhibits significant coherency 80 ci only at periods 5 4 years and 2 7 years suggesting the significant role of enso dynamics in organizing the subtle indian monsoon at these frequencies these results may provide significant implication for the modeling of indian monsoon

age and duration of activity at the isle of mull tertiary igneous centre scotland and confirmation of the existence of subchrons during anomaly 26r the duration of activity that produced the isle of mull tertiary igneous centre has been constrained to 2 52 0 36 million years 1 using new high resolution 40ar 39ar radiometric dating techniques these new 40ar 39ar ages for mull and also one from skye presented here confine the duration of igneous activity to within one magnetic chron 3 million years within chron c26r however the mull and skye tertiary centres record a sequence of reversed and normal polarity intervals recalibration of tie points used to determine the magnetic polarity time scale cannot account for all of the observed changes in polarity from mull and skye we propose that the new ages for the mull and skye centres indicate that these parts of the british tertiary volcanic province developed fast enough to record short period polarity intervals which correspond to tiny wiggles in the marine magnetic anomaly record

hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth order stream in brittany france three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth order stream in brittany western france i an upland flow that supplied a wetland area mainly during the high water period it has high n no3 and average cl concentrations ii a deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling iii an unconfined aquifer under the riparian zone with high cl and low n no3 concentrations where biological processes removed groundwater nitrate this aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone patterns of n no3 and cl concentrations along riparian transects together with calculated high nitrate removal indicate that removal occurred mainly at the hillslope riparian zone interface i e first few metres of wetland whereas dilution occurred in lower parts of the transects especially during low water periods and at the beginning of recharge periods stream flow was modelled as a mixture of water from the three reservoirs an estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37 throughout the study period while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable from ca 6 to 85 relative to rainfall events and the level of the riparian water table at the entire riparian zone scale no3 removal probably from denitrification appeared most effective in winter despite higher estimated upland no3 fluxes entering the riparian zone during this period copyright 2003 john wiley sons ltd

magmatic like fluid source of the chingshui geothermal field ne taiwan evidenced by carbonate clumped isotope paleothermometry abstract the chingshui geothermal field a moderate temperature and water dominated hydrothermal system was the site of the first geothermal power plant in taiwan many geological geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s however there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting to clarify the heat and fluid sources we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the 18 o values of the source fluids two populations of 18 o values were calculated 5 8 0 8 vsmow from scaling in the well and 1 0 1 6 to 10 0 1 3 vsmow from outcropping calcite veins indicative of meteoric and magmatic fluid sources respectively meanwhile two hydrothermal reservoirs at different depths have been identified by magnetotelluric mt imaging with micro seismicity underneath this area as a result we propose a two reservoir model the shallow reservoir provides fluids from meteoric water for the scaling sampled from wells whereas the deep reservoir provides magmatic fluids from deep marble decarbonization recorded in outcropping calcite veins

la icp ms u pb geochronology and clumped isotope constraints on the formation and evolution of an ancient dolomite reservoir the middle permian of northwest sichuan basin sw china abstract recent advances in laser ablation inductively coupled plasma mass spectrometry la icp ms in situ u pb radiometric dating and clumped isotope thermometry 47 of carbonate minerals provide potential for refining the fluid flow and diagenetic history of carbonate successions in this study the middle permian dolomites proximal to the longmenshan fold and thrust belt in northwest sichuan basin southwest china were investigated using combined u pb geochronology clumped isotope thermometry and routine isotopic 13c 18o and 87sr 86sr and elemental geochemistry in an attempt to reveal the possible relevance of carbonate diagenesis and porosity evolution to the basin scale tectonic fluid flow events in the framework of absolute time overall formation and evolution of these dolomites temporally correlated well with major tectonic episodes of the longmenshan fold and thrust belt contrary to the previously assumed volcanic related model u pb dating and 47 analyses suggest a mid to late triassic replacive dolomitization event u pb ages of 240 12 ma to 233 8 6 4 ma by a hot 47 temperatures 88 104 c basinal brine which was likely driven by thrust related compression of the longmenshan fold and thrust belt during the triassic replacive dolomitization was immediately followed by cementation of euhedral dolomites u pb age of 228 10 ma and blocky calcites u pb ages of 224 8 1 8 ma to 213 4 3 3 ma precipitated from the basinal brine in the same tectonic regime afterwards there was long term cessation of diagenesis that was coincident with and thus may well be attributed to tectono thermal quiescence during most of the mesozoic era and paleogene finally saddle dolomite cements yield miocene ages u pb ages of 16 40 0 74 ma to 12 3 1 2 ma and precipitated in pre existing vugs representing a hydrothermal fluid flow event 47 temperatures up to 170 c during the reactivation of thrusting in addition similarities in u pb ages and geochemical signatures between host rocks replacive dolomites and the vug lining dolomite cements suggest that most porosity in these dolomite reservoirs was inherited from the precursor limestones which probably experienced meteoric leaching during late permian uplift this study highlights that there are geodynamic controls on fluid flow and consequent diagenetic evolution of carbonates in tectonically active sedimentary basins it illustrates that burial alone in this setting is not a sufficient driver for diagenetic alteration and porosity reduction the combination of u pb radiometric dating clumped isotope thermometry and routine geochemical analyses is a useful approach in refining the diagenetic and porosity evolution history of ancient carbonate successions

paleoclimatic implications of holocene plant remains from the sierra bacha sonora mexico abstract a total of 93 plant taxa were identified from 11 packrat neotoma sp midden samples from the sierra bacha on the coast of the gulf of california near puerto libertad sonora mexico nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr b p sonoran desertscrub was present on rocky slopes throughout the holocene early holocene assemblages dominated by fouquieria columnaris boojum tree reflect vegetation and climate more like modern baja california with greater winter rainfall and cooler summers middle holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold water upwelling locally inhibits summer precipitation the results are similar to all previous midden reconstructions of early and middle holocene climates in the sonoran desert but contradict general atmospheric circulation model simulations

temperature dependence of the oxygen isotopic fractionation between diatom silica and water abstract we present a new paleotemperature scale based on the oxygen isotopic ratio of the non exchangeable fraction of the oxygen from diatom silica the equation t 17 2 2 4 18osilica 18owater 40 0 2 18osilica 18owater 40 2 was derived using recent sediment samples from different oceanic areas the temperature and isotopic composition of the local surface water comparison of our results with other relationships established for quartz water or amorphous silica water at higher temperature suggests no difference in isotopic fractionation between quartz water and biogenic silica water couples

geochemical cycles in sediments deposited on the slopes of the guaymas and carmen basins of the gulf of california over the last 180 years sediments deposited on the slopes of the guaymas and carmen basins in the central gulf of california were recovered in two box cores q mode factor analyses identified detrital clastic carbonate and redox associations in the elemental composition of these sediments the detrital clastic fraction appears to contain two source components a more mafic component presumably derived from the sierra madre occidental along the west coast of mexico and a more felsic component most likely derived from sedimentary rocks mostly sandstones of the colorado plateau and delivered by the colorado river the sediments also contain significant siliceous biogenic components and minor calcareous biogenic components but those components were not quantified in this study redox associations were identified in both cores based on relatively high concentrations of molybdenum which is indicative of deposition under conditions of sulfate reduction decreases in concentrations of molybdenum in younger sediments suggest that the bottom waters of the gulf have became more oxygenated over the last 100 years many geochemical components in both box cores exhibit distinct cyclicity with periodicities of 10 20 years the most striking are 20 year cycles in the more mafic components e g titanium particularly in sediments deposited during the 19th century in that century the titanium cycles are in very good agreement with warm phases of the pacific decadal oscillation implying that at times of greater influx of titanium rich

correlation of nitrate profiles with groundwater and sediment characteristics in a shallow sandy aquifer abstract sediment profiles of a shallow sandy aquifer in an agricultural area of denmark can be characterized by a new term called total reduction capacity trc quantifying the total amount of reduced compounds in the aquifer material ferrous iron reduced sulfur compounds solid organic carbon a distinct increase of trc was observed at and below the oxidation reduction front in this study the front was a zone 30 cm wide oxygen nitrate and sulfate were present above the oxidation reduction front but disappeared at the front detailed porewater profiles indicate that denitrification also takes place above the front supposedly in anaerobic microenvironments not evident in the water samples from the small wells the trc profiles showed that some reduction capacity is still present above the oxidation reduction front and is apparently able to support denitrification

hydrologic variability and the onset of modern el nino southern oscillation a 19 250 year record from lake elsinore southern california there are very few terrestrial palaeoclimate archives spanning the last glacial maximum through the holocene from coastal southern california yet knowledge of past climate dynamics is critical for assessing present and future constraints on the region s dwindling freshwater resources we present initial results from two drill cores extracted from the present day edge of lake elsinore southern california s largest natural lake using a multiproxy approach including lithologic description mass magnetic susceptibility loi 550 c total organic matter and loi 950 c total carbonate we infer first order long term climate change over the past 19 250 calendar years furthermore we suggest possible first order forcing mechanisms that drive this change which include presence absence of continental ice sheets insolation and complex ocean atmosphere interactions our results indicate four distinct millennial scale climate modes over the past 19 250 calendar years these modes include a wet last glacial maximum 19 250 17 120 cal yr bp a relatively dry late glacial holocene transition 17 120 9450 cal yr bp a wet early holocene 9450 7670 cal yr bp and a highly variable mid to late holocene climate i e alternating wet dry cycles 7670 cal yr bp present we attribute the mid to late holocene climate interval to the onset of el nino southern oscillation ca 7000 cal yr bp and a more vigorous hydrologic system these results are supported by a variety of regional terrestrial and marine palaeoclimate archives copyright 2005 john wiley sons ltd

the onset of the dead sea transform based on calcite age strain analyses the onset and evolution of the dead sea transform are re evaluated based on new in situ u pb dating and strain analyses of mechanically twinned calcites direct dating of 30 syn faulting calcites from 10 different inactive fault strands of the transform indicates that the oceanic to continental plate boundary initiated between 20 8 and 18 5 ma within an 10 km wide distributed deformation zone in southern israel ages from the northern dead sea transform 17 1 12 7 ma suggest northward propagation and the establishment of a well developed 500 km long plate bounding fault in 3 m y the dominant horizontal shortening direction recorded in the dated twinned calcites marks the onset of left lateral motion along the evolving plate boundary the observed changes in the strain field within individual fault strands cannot be simply explained by local weakening effects along strands of the dead sea transform or by gradual changes in the euler pole through time

clumped isotope palaeothermometry and la icp ms u pb dating of lava pile hydrothermal calcite veins calcite veins are a common product of hydrothermal fluid circulation clumped isotope palaeothermometry is a promising technique for fingerprinting the temperature of hydrothermal fluids but clumped isotope systematics can be reset at temperatures of ca 100 c to model whether the reconstructed temperatures represent calcite precipitation or closed system resetting the precipitation age must be known la icp ms u pb dating of calcite is a recently developed approach to direct dating of calcite and can provide precipitation ages for modelling clumped isotope systematics in calcite veins in this study clumped isotope and la icp ms u pb calcite analyses were combined in basalt hosted calcite veins from three settings in scotland samples from all three localities yielded precipitation temperatures of ca 75 115 c from clumped isotope analysis but veins from only two of the sites were dateable yielding precipitation ages of 224 8 ma and 291 33 ma 2 modelling from the dated samples enabled confident interpretation that no closed system resetting had occurred in these samples however the lack of a precipitation age from the third location meant that a range of possible thermal histories had to be modelled meaning that confidence that resetting had not occurred was lower this highlights the importance of coupling clumped isotope thermometry and la icp ms u pb calcite dating in determining the temperature of hydrothermal fluids recorded in calcite veins this paired approach is shown to be robust in constraining the timing and precipitation temperature of calcite formation and thus for tracking hydrothermal processes

laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25 250 c temperature range abstract many fields of earth sciences benefit from the knowledge of mineral formation temperatures for example carbonates are extensively used for reconstruction of the earth s past climatic variations by determining ocean lake and soil paleotemperatures furthermore diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution it is based on the temperature dependent abundance of the rare 13c 18o bonds in carbonate minerals specified as a 47 value the clumped isotope thermometer has been calibrated experimentally from 1 c to 70 c however higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory in order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high temperature geological processes we precipitated caco3 mainly calcite in the laboratory between 23 and 250 c we used two different precipitation techniques first minerals were precipitated from a caco3 supersaturated solution at atmospheric pressure 23 91 c and second from a solution resulting from the mixing of cacl2 and nahco3 in a pressurized reaction vessel at a pressure of up to 80 bar 25 250 c the calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 c our study suggests a universal 47 t calibration t in k 47 in 47 0 98 0 01 3 407 10 9 t 4 2 365 10 7 t 3 2 607 10 3 t 2 5 880 t 0 293 0 004 this new 47 t calibration given in the absolute reference frame that extends the experimentally calibrated temperature range for clumped isotopes to 250 c can be applied to carbonates that grew at intermediate temperatures 20 250 c

late stage anhydrite gypsum siderite dolomite calcite assemblages record the transition from a deep to a shallow hydrothermal system in the schwarzwald mining district sw germany abstract the majority of hydrothermal vein systems of economic interest occur at relatively shallow crustal levels although many of them formed at significantly greater depths their present position is a consequence of uplift and erosion although many aspects of their formation are well constrained the temporal chemical evolution of such systems during uplift and erosion is still poorly understood these vein minerals comprise calcite dolomite ankerite siderite magnesite anhydrite and gypsum forming the last gangue assemblages in jurassic and tertiary sulphide fluorite quartz barite veins of the schwarzwald mining district sw germany mineral textures of samples from nine localities reveal that in these sequences mineral precipitation follows a recurring pattern early calcite is followed by anhydrite or gypsum siderite and or dolomite this succession may repeat up to three times in situ la icp ms u pb age dating of 15 carbonates from three subsequent generations of the late stage vein assemblage yield robust ages between 20 and 0 6 ma each mineral sequence forms in a distinctive period of about 2 5 ma these ages clearly relate these late stage mineral phases to the youngest geological episode of the schwarzwald which is associated with the cenozoic rhine graben rifting and basement uplift based on thermodynamic modelling the formation of the observed mineral assemblages required an deeply sourced mg fe and so4 rich fluid b which was episodically mixed with a shallow crustal hco3 rich fluid a as a consequence of fluid mixing concentrations of mg fe and so4 temporarily increased and initiated the formation of the observed sulphate carbonate mineral sequences this discontinuous large scale vertical fluid mixing was presumably directly related to episodes of active tectonics associated with the cenozoic strike slip regime of the upper rhine graben analogously episodic fluid mixing is a major key in the formation of older jurassic to early tertiary pb zn fluorite quartz barite assemblages in the same specific vein systems albeit involving different fluid compositions late stage hydrothermal 20 70 c vein assemblages reported in this study record the transition from deep 2 km to very shallow 0 1 km crustal conditions as a consequence of successive uplift increasing proportions of shallower and cooler 50 70 c fluids could take part in such mixing processes associated changes in the fluid composition caused the vein mineralogy to change from sulphide quartz fluorite barite to calcite anhydrite gypsum siderite dolomite as the system passively ascended closer to the surface

isotopic evidence for microbial production and consumption of methane in the upper continental crust throughout the phanerozoic eon microorganisms produce and consume methane in terrestrial surface environments sea sediments and as indicated by recent discoveries in fractured crystalline bedrock these processes in the crystalline bedrock remain however unexplored both in terms of mechanisms and spatiotemporal distribution here we have studied these processes via a multi method approach including microscale analysis of the stable isotope compositions of calcite and pyrite precipitated in bedrock fractures in the upper crust down to 1 7 km at three sites on the baltic shield microbial processes have caused an intriguing variability of the carbon isotopes in the calcites at all sites with 13c spanning as much as 93 1 related to anaerobic oxidation of methane to 36 5 related to methanogenesis spatiotemporal coupling between the stable isotope measurements and radiometric age determinations micro scale dating using new high spatial methods la icp ms u pb for calcite and rb sr for calcite and co genetic adularia enabled unprecedented direct timing constraints of the microbial processes to several periods throughout the phanerozoic eon dating back to devonian times these events have featured variable fluid salinities and temperatures as shown by fluid inclusions in the calcite dominantly 70 85 c brines in the paleozoic and lower temperatures 50 62 c and salinities in the mesozoic preserved organic compounds including plant signatures within the calcite crystals mark the influence of organic matter in descending surficial fluids on the microbial processes in the fracture system thus linking processes in the deep and surficial biosphere these findings substantially extend the recognized temporal and spatial range for production and consumption of methane within the upper continental crust

a calcite reference material for la icp ms u pb geochronology u pb dating of calcite is an emerging but rapidly growing field of application in geochronology with great potential to inform problems in landscape basin and mountain belt evolution through age determination of diagenetic cements vein mineralisation and geological formations difficult to date otherwise in this brief we present isotope dilution u pb isotope measurements on a sample of calcite wc 1 that has been and will continue to be used as a reference material for in situ u pb laser ablation inductively coupled plasma mass spectrometry la icp ms dating and which is suitable to be distributed to the geochronological community we present in situ measurements using la icp ms to demonstrate the suitability of wc 1 for use as a u pb dating reference material in spite of it not being isotopically homogeneous the wc 1 calcite sample is 254 4 6 4 ma old and comprised of 85 to 98 radiogenic lead it presents a suitable reference material that can facilitate dating of calcite ranging in age from precambrian to late neogene age

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

30 000 years of hydrothermal activity at the lost city vent field strontium carbon and oxygen isotope data and radiocarbon ages document at least 30 000 years of hydrothermal activity driven by serpentinization reactions at lost city serpentinization beneath this off axis field is estimated to occur at a minimum rate of 1 2 10 4 cubic kilometers per year the access of seawater to relatively cool fresh peridotite coupled with faulting volumetric expansion and mass wasting processes are crucial to sustain such systems the amount of heat produced by serpentinization of peridotite massifs typical of slow and ultraslow spreading environments has the potential to drive lost city type systems for hundreds of thousands possibly millions of years

planktonic foraminiferal faunal and stable isotopic indices of upwelling a sediment trap study in the san pedro basin southern california bight

the response of equatorial oceans to a relaxation of the trade winds abstract the trade winds over the central pacific are observed to weaken several months after the appearance of anomalously warm surface waters in the eastern equatorial pacific ocean the following results obtained with a numerical model indicate how this relaxation of the winds affect the later stages of el nino a weakening of the westward trade winds causes a zonal redistribution of heat in the equatorial oceans and a warming of the eastern part of the basin the warming depends on the zonal extent of the region over which the winds relax and on the length of time t for which the winds relax as t increases the warming in the east increases until it asymtotes to a maximum value when t exceeds the adjustment time of the basin which is 400 days in the case of the pacific ocean maximum heating is associated with a permanent weakening of the winds unless the winds reverse direction and become eastward even weak eastward winds for a short period can cause disproportionately large temperature increa

temperature variability in the gulf of california during the last century a record of the recent strong el nino the oxygen isotopic ratio of diatom silica from a box core collected on the eastern slope of the guaymas basin gulf of california has been analyzed this core covers the last 90 years the isotopic record indicates a progressive and continuous temperature increase of about 8 c from the end of the last century until 1980 with superimposed rapid temperature fluctuations of 2 to 4 c although the gulf of california is not directly under the influence of el nino short temperature increases may be associated with the el nino events described by quinn et al 1987 the longer term changes are attributed to a decrease of upwelling intensity linked to weakening of the trade winds in the northern hemisphere

a 20 year varve record of siliceous phytoplankton variability in the central gulf of california abstract year to year variability in the structure of the preserved siliceous phytoplankton assemblage is reconstructed from a box core retrieved from the varved sediments along the guaymas slope of the gulf of california a 20 year record from 1953 through 1972 is obtained from interpretation of the varve stratigraphy supported by 210 pb and 228 th dating ecological time series derived from microfossil analysis show a strong coherence with interannual sea level anomalies indicating a response to large scale climatic variability associated with the el nino southern oscillation phenomenon el nino periods are generally marked by increases in preserved abundances of the total siliceous assemblage and in particular by greater numbers of individuals within species whose distribution is limited to tropical and subtropical waters

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

absolute ages of multiple generations of brittle structures by u pb dating of calcite direct dating of brittle structures is challenging especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events we report 22 calcite u pb ages from tec

the effect of species on lacustrine δ18odiatom and its implications for palaeoenvironmental reconstructions the oxygen isotope composition of diatom silica 18odiatom is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom we present 18odiatom data from two diatom size fractions 3 38 and 38 m characterized by different species in a sediment core from heart lake alaska differences in 18odiatom between the two size fractions varies from 0 to 1 2 with a mean offset of 0 01 n 20 fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica sio2 and 18odiatom trends are not driven by contamination the maximum offset is outside the range of error but the mean is within analytical error of the technique 1 06 demonstrating no discernible species dependent fractionation in 18odiatom we conclude that lacustrine 18odiatom measurements offer a reliable and valuable method for reconstructing 18owater considering the presence of small offsets in our two records we advise interpreting shifts in 18odiatom only where the magnitude of change is greater than the combined analytical error

measuring plume related exhumation of the british isles in early cenozoic times mantle plumes have been proposed to exert a first order control on the morphology of earth s surface however there is little consensus on the lifespan of the convectively supported topography here we focus on the cenozoic uplift and exhumation history of the british isles while uplift in the absence of major regional tectonic activity has long been documented the causative mechanism is highly controversial and direct exhumation estimates are hindered by the near complete absence of onshore post cretaceous sediments outside northern ireland and the truncated stratigraphic record of many offshore basins two main hypotheses have been developed by previous studies epeirogenic exhumation driven by the proto iceland plume or multiple phases of cenozoic compression driven by far field stresses here we present a new thermochronological dataset comprising 43 apatite fission track aft and 102 u th sm he ahe dates from the onshore british isles inverse modelling of vertical sample profiles allows us to define well constrained regional cooling histories crucially during the paleocene the thermal history models show that a rapid exhumation pulse 1 2 5 km occurred focused on the irish sea exhumation is greatest in the north of the irish sea region and decreases in intensity to the south and west the spatial pattern of paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies and the timing of uplift and exhumation is synchronous with emplacement of the plume related british and irish paleogene igneous province bipip prior to the paleocene exhumation pulse the mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long lived rifting history of the neighbouring offshore basins the extent of neogene exhumation is difficult to constrain due to the poor sensitivity of the ahe and aft systems at low temperatures we conclude that the cenozoic topographic evolution of the british isles is the result of plume driven uplift and exhumation with inversion under compressive stress playing a secondary role

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

palynological record 1483 1994 of gymnodinium catenatum in pescadero basin southern gulf of california mexico article i nfo this paper presents the stratigraphic record of gymnodinium catenatum during the last 500 years in pescadero basin southern gulf of california our aim is to help clarify the relation between abundances of cysts of g catenatum and regional changes in the sea surface temperature and nutrient availability at a decadal scale the record was obtained from core samples of laminated sediments dated with 14 c

geochronology of carboniferous permian magmatism in the midland valley of scotland implications for regional tectonomagmatic evolution and the numerical time scale four new u pb isotope dilution thermal ionization mass spectrometry dates from carboniferous igneous rocks of the midland valley of scotland are integrated with 16 recently published 40ar 39ar dates the numerical and stratigraphical ages of the dated samples are compatible to stage level allowing improved intrabasinal and regional correlations early carboniferous extension related volcanism in the midland valley was pulsed with a date of 343 4 1 0 ma from the garleton hills volcanic formation and dates of 334 7 1 7 and 335 2 0 8 ma from the clyde plateau volcanic formation the magmatic pulses are synchronous with synrift phases in the northumberland solway basin volcanism continued in mid to late carboniferous time contemporaneous with dextral strike slip tectonics in contrast to a post rift tectonic setting in northern england after late carboniferous basin inversion tholeiitic magmatism dated at 307 6 4 8 ma provides a maximum westphalian d age for post variscan magmatism and extension dextral transtension across scotland and northern england in the early permian as rift systems developed across nw europe alkaline extension related magmatism resumed in the midland valley from c 298 to 292 ma the improved geochronology provides important data for poorly constrained parts of the numerical carboniferous time scale such as stages within the visean and provides a well controlled tie point that supports a tournaisian visean boundary age of c 345 4 ma

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

brief duration of hydrothermal activity at round mountain nevada determined from ar 40 ar 39 geochronology the round mountain gold silver deposit is one of the world s largest volcanic hosted precious metal deposits reserves plus production total at least 16 million oz 500 000 kg au the deposit occurs in ash flow tuff that is ponded within its source caldera along and overlying the caldera ring fracture host rocks have undergone propylitic potassic and high level silicic and intermediate argillic alteration these are interpreted either as a temporal sequence from early propylitic to late silicic and argillic or as a spatial progression from a potassic core outward to a propylitic halo 40 ar 39 ar ages determined by single crystal fusion of sanidine from host tuff and incremental heating of adularia indicate a most likely duration of hydrothermal activity of approximately 0 1 m y possibly no more than 0 05 m y and a maximum of 0 5 m y eruption of host ash flow tuff and caldera collapse occurred at 26 5 ma a late or postalteration tuff that rests upon mineralized rock is 26 0 ma hydrothermal circulation is unlikely to have been established immediately after caldera collapse so duration was probably considerably less than 0 5 m y eight adularia samples give ages between 25 94 or 0 09 and 26 09 or 0 05 ma and one is 26 20 or 0 05 ma the mean of all nine is 26 03 or 0 08 ma the maximum and minimum values and their uncertainties allows a duration of as much as 0 4 m y but for the following reasons the longevity is probably much less the absolute ages of seven samples that can be placed in the possible temporal alteration sequence do not correlate with that sequence this does not disprove the temporal sequence but does indicate that alteration occurred in a time span which is not resolvable even with precise 40 ar 39 ar dating furthermore all samples show flat age spectra which themselves argue against a long continuously active system kinetic studies of two adularia reveal diffusion domains with ar closure temperatures between approximately 230 degrees and approximately 390 degrees c adularia that crystallized and remained at temperatures of 275 degrees c the maximum temperature inferred from fluid inclusion data would yield age spectra with age gradients spanning the lifetime of the system no spectra are consistent with a thermal history that incorporates sustained 0 1 m y temperatures at or above 275 degrees c episodic activity to account for the one older adularia date cannot be precluded but is inconsistent with most data therefore the hydrothermal system probably was active for less than the uncertainty in the ages of individual samples possibly as little as 50 000 years we conclude that hydrothermal activity at round mountain was a brief event at approximately 26 0 ma and was closely linked to caldera structure and magmatism this activity followed initial ash flow eruption by 0 5 m y and may have been driven by a ring fracture intrusion

methane and the origin of five element veins mineralogy age fluid inclusion chemistry and ore forming processes in the odenwald sw germany abstract five element veins ag bi co ni as have been valuable mineral deposits since medieval times the characteristic occurrence of large aggregates of native metals up to several dm surrounded by a succession of arsenides makes this vein type attractive for mining industry natural history museums and private mineral collectors nevertheless the exact formation process of these specific vein types has not been fully understood this is the first case study applying a new model which includes methane as a reducing agent to two typical examples of such mineralisations from the odenwald sw germany we analysed all mineralogical varieties ag as and bi dominated of the five element veins in the odenwald sw germany in terms of ore textures mineral chemistry fluid inclusion compositions microthermometry and raman spectroscopy stable isotopes c o and s and in situ u pb age dating of calcite and prehnite a variety of ag bi and as dominated native metal arsenide calcite veins sulphide calcite veins and arsenide free ag hg barite veins occurs in the odenwald and has been examined in this study all arsenide veins have in common that up to dm sized often dendritic native metals are overgrown by a succession of arsenides followed by carbonate and finally sulphides the succession of arsenides shows a distinct spatial and temporal chemical trend in their composition this trend evolves from ni to co and finally fe dominated compositions from the core to the rim in contrast spatially closely related ag hg barite veins consist of almost mono mineralic amalgam inter grown with barite in situ u pb age dating of low u calcite and prehnite was applied to constrain the age of hydrothermal mineralisation the results imply that the five element veins formed at 170 180 ma from na ca cl fluids at 290 c salinities of 27 wt and ca ca na of 0 30 to 0 35 in the presence of methane the age data clearly relate the relevant fluid migration to extension and crustal thinning caused by the opening of the north atlantic ternary mixing of a deep seated metal rich basement brine fluid a a sulphide bearing h2s and hs basinal sedimentary brine fluid b and methane dominated fluid gas fluid c induce ore formation mixing of such chemically contrasting fluids results in a strong chemical disequilibrium of the mixed fluid which potentially leads to rapid precipitation of native metals and arsenides with these specific ore textures in contrast sulphide bearing calcite veins formed under similar p t conditions due to mixing of fluid a and b while fluid c was absent additionally u pb analyses of post ore calcite yields ages of 60 ma which indicates that a second calcite formation event is associated with the onset of the upper rhine graben rifting veins with amalgam and barite form as a consequence of post ore oxidation of ag2s at 135 c conspicuously this secondary silver ii has hg contents of up to 30 wt in contrast to hg contents below 1 wt of primary silver i and ag2s the formation of amalgam was most likely related to decrease of the s2 so42 ratio due to cooling of the late hydrothermal fluid resulting in the destabilisation of hg bisulphide complexes in this fluid

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate based standardization about a decade after its introduction the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long standing questions in earth sciences major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations the relatively complex sample preparation procedures and the mass spectrometric corrections needed in this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty we propose that the use of carbonate standards to project the results to the carbon dioxide equilibrium scale can improve interlaboratory data comparability and help to solve long standing discrepancies between laboratories and temperature calibrations the use of carbonates reduces uncertainties related to gas preparation and cleaning procedures and ensures equal treatment of samples and standards we present a set of carbonate standards of diverse composition discuss how they can be used to correct for mass spectrometric biases and demonstrate that their use significantly improves the comparability among four laboratories we propose that the use of these standards or of a similar set of carbonate standards will improve the comparability of data across laboratories

40ar 39ar geochronology of carboniferous permian volcanism in the midland valley scotland twenty one new 40 ar 39 ar step heating experiments on mineral separates from intrusive and extrusive carboniferous and permian igneous rocks in the midland valley of scotland yielded 17 concordant experiments with a relative age precision better than 1 2 these ages resolve inconsistencies between existing k ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales the precise 40 ar 39 ar dates are stratigraphically constrained to stage level and can contribute to carboniferous timescale tie points at the tournaisian visean boundary within the visean and at the carboniferous permian boundary situated in the extending variscan foreland two distinct phases of extension related transitional alkaline volcanism have been resolved in the dinantian the garleton hills volcanic formation in the eastern midland valley near the tournaisian visean boundary 342 1 1 3 and 342 4 1 1 ma and the clyde plateau volcanic formation in the western midland valley during the mid visean 335 2 329 2 1 4 ma alkaline basic sills near edinburgh previously thought to be namurian appear to be coeval with the clyde plateau volcanic formation at 331 8 1 3 329 3 1 5 ma the new ages allow correlation between these short lived dinantian magmatic pulses and extensional and magmatic phases in the northumberland solway and tweed basins to the south after late westphalian end variscan compression and a regionally important tholeiitic intrusive phase at c 301 295 ma alkaline magmatism related to post variscan extension occurred in the central and western midland valley during the latest carboniferous or permian from 298 3 1 3 to 292 1 1 1 ma this correlates well with post varsican extension and magmatism observed across the nw european foreland from 300 to 280 ma

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

u pb dating of geodic calcite new insights on western europe major tectonic events and associated diagenetic fluids this study presents the first application of the u pb dating method to highly pb depleted diagenetic geodic calcites of the jurassic formations of the paris basin that leads to a reappraisal of the palaeohydrological history of this region composite u pb ages from multiple geodes combined with 18 o analyses reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events dogger formations recorded a first diagenetic fluid episode at 147 8 3 8 ma i e at the very beginning of the emersion of the basin during the tithonian period and 30 ma earlier than previously assumed 18 o results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the cretaceous period oxfordian formations recorded another major meteoric fluid circulation at 33 5 2 8 ma related to the initial stage of the european cenozoic rift system ecris consequently the porosity of the mesozoic formations of the studied area may have been closed sooner than previously thought before the main ecris rifting phase of oligocene age this study shows that u pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins supplementary material pb pb diagrams 238 u and 235 u series isochron diagrams and effect of blank correction on u and pb isotopic compositions and on ages calculation are available at https doi org 10 6084 m9 figshare c 3886885

emplacement related fault patterns around the northern granite arran scotland conspicuous faults in the new red sandstone nrs mainly permian triassic of arran are shown to be kinematically related to the intrusion of the northern granite in paleocene time early inflation of the granite pluton in the upper crust induced radial stretching in the overlying sedimentary cover recorded in predominantly normal offsets on the faults in the nrs continued ballooning of the pluton superimposed strong concentric dip slip displacement over its flanks both stretching and uplift were heterogeneous strongly controlled by a nonuniform stratigraphy and by reactivation of older faults striking predominantly north northwest and northeast and dating back at least to permian time the paleocene displacements on these discrete weak sub nrs faults diffused upward through nrs sandstones on numerous minor faults each with only small offset this behavior resulted from slip hardening on each fault in the poorly cemented nrs rocks late in the intrusion history the major faults on the southeast side of the granite formed a conjugate strike slip system that accommodated radial expansion of the pluton mainly during intrusion of a discrete magma batch that now forms the inner fine grained granite other structures around and within the northern granite are shown to be more compatible with this two stage ballooning model than with a vertical plug emplacement model previous assessments of the ballooning process in general have been made on deep level lateral margins of plutons where radial shortening dominates in the envelope north arran is an important example of the complexities of ballooning at shallow levels in a heterogeneous crust

distribution of silicoflagellates in plankton and core top samples from the gulf of california plankton and surface sediment samples from the gulf of california were examined to determine the present geographic distribution of silicoflagellate species in this area variations in the species composition of the silicoflagellate assemblage were found to be related to water mass distributions eight species were identified in these samples octactis pulchra is associated with high levels of primary productivity in the surface waters and is found in greatest abundance in the central gulf of california dictyocha messanensis dominates the silicoflagellate assemblage in stations outside the gulf of california and increases in relative abundance with decreasing amounts of octactis pulchra dictyocha calida dictyocha sp a and dictyocha sp b are associated with equatorial waters and have the highest relative abundance near the mouth of the gulf dictyocha epiodon and distephanus speculum are associated with cold california current water and dictyocha epiodon is present in minor abundance in gulf samples dictyocha sp 2 has a patchy distribution with low relative abundance

rapid middle eocene temperature change in western north america abstract eocene hyperthermals are among the most enigmatic phenomena of cenozoic climate dynamics these hyperthermals represent temperature extremes superimposed on an already warm eocene climate and dramatically affected the marine and terrestrial biosphere yet our knowledge of temperature and rainfall in continental interiors is still rather limited we present stable isotope 18o and clumped isotope temperature 47 records from a middle eocene 41 to 40 ma high elevation mammal fossil locality in the north american continental interior montana usa 47 paleotemperatures of soil carbonates delineate a rapid 9 11 c temperature excursion in the paleosol record 47 temperatures progressively increase from 23 c 3 c to peak temperatures of 32 c 3 c and subsequently drop by 11 c this hyperthermal event in the middle eocene is accompanied by low 18o values and reduced pedogenic carbonate concentrations in paleosols based on laser ablation u pb geochronology of paleosol carbonates in combination with magnetostratigraphy biostratigraphy stable isotope and 47 evidence we suggest that this pronounced warming event reflects the middle eocene climatic optimum meco in western north america the terrestrial expression of northern hemisphere meco in western north america appears to be characterized by warmer and wetter sub humid conditions compared to the post meco phase large and rapid shifts in 18o values of precipitation and pedogenic caco3 contents parallel temperature changes indicating the profound impact of the meco on atmospheric circulation and rainfall patterns in the western north american continental interior during this transient warming event

an emerging thermochronometer for carbonate bearing rocks 47 u pb assessing the thermal evolution of sedimentary basins is critical for understanding the origin of natural resources including ores geothermal fluids or hydrocarbons and for deciphering larger scale tectonic and geodynamic evolutions modern reconstructions of past subsurface temperatures mostly rely on thermochronometers that are not applicable to carbonate rocks e g fission track and u th he analyses here by coupling carbonate clumped isotope 47 thermometry and laser ablation u pb geochronology on a complete paragenetic sequence we demonstrate the applicability of an emerging thermochronometer for carbonate bearing rocks paired 47 and u pb data were obtained for calcite and dolomite phases precipitated in a middle jurassic carbonate hydrocarbon reservoir of the paris basin depocenter france the absolute thermochronological data allow the precise reconstruction of the thermal history of these rocks from shallow burial temperatures 40 c occurring in the late jurassic toward a progressive burial and heating stage up to 87 c during the cretaceous followed by a cooling stage down to 69 c during the tertiary uplift of the basin the inferred time temperature path based on 47 u pb data is mostly consistent with the thermal scenario independently deduced from organic maturity indicators from the underlying lower jurassic shales the 47 u pb thermochronological data also highlight a thermal anomaly during aptian albian time that requires revisiting the accepted timing for hydrocarbon migration in the middle jurassic reservoir carbonates

varve formation in the gulf of california insights from time series sediment trap sampling and remote sensing the varved sediments that accumulate in the central gulf of california guaymas and carmen basins provide a record that allows for the resolution of annual to decadal scale climate variability in this region time series sediment trapping combined with remotely sensed observations of sea surface temperature avhrr and color czcs have been used to examine the mechanism of varve formation in the central gulf sst and surface pigment concentration records for both the mainland and baja sides of the gulf display similar seasonal trends high temperatures and low pigment concentrations occur synchronously on both sides of the central gulf from june through to october in association with the 1991 92 el nino warm temperatures persist in the central gulf until december low ssts typically occur from december through may with high pigment concentrations marking the period from november through april the summer early fall june october is a time of high terrigenous and biogenic sediment fluxes during this time of year the total flux is dominated by eolian transported lithogenic material and dark laminae are deposited during this period during el nino years high terrigenous fluxes may extend into winter light laminae represent deposition from november through may during which time biogenic material dominates the total sediment flux high opal fluxes beginning in november are attributed to seasonal cooling of surface water and upward mixing of nutrients true upwelling conditions do not develop in the gulf until late winter spring during this time the total flux is still dominated by opal but the magnitude of the flux is reduced this may be an artifact of phytoplankton grazing and not lower production rates

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

deciphering the diagenetic history of the el abra formation of eastern mexico using reordered clumped isotope temperatures and u pb dating carbonates form ubiquitously throughout the history of deposition burial and uplift of basins as such they potentially record the environmental conditions at the time of formation carbonate clumped isotopes provide the temperature of precipitation but can be internally reordered if the host rock is exposed to elevated temperatures over geologic time scales here we exploited this kinetic behavior by analyzing multiple generations of cements that capture the range of environments experienced by the el abra formation from eastern mexico from this we developed a quantitative diagenetic history for these different phases of cementation we observed a 70 c range in clumped isotope temperatures from 64 c to 134 c for these cements which is not compatible with their inferred precipitation environments this suggests that bond reordering occurred during burial but did not fully reorder all cements to a common apparent temperature we reconstructed original cement growth temperatures and the isotopic signature of the parent fluids to show that precipitation from a marine pore fluid began at 125 ma contemporaneous with deposition and continued throughout burial to temperatures of at least 138 c at 42 ma we show that precipitation of equant cements which occluded 90 of the pore space was coincident with laramide related burial to depths greater than 3800 m a u pb age of diagenetic calcite of 77 1 3 6 ma provides independent support for our estimates of the absolute timing of precipitation of two distinct phases of the paragenesis this is the first demonstration of the utility of integrating u pb age dating with reordered clumped isotope temperatures to provide quantitative constraints on the time temperature history of cementation such information may ultimately lead to advances in our understanding of the formational environments and geological processes that drive diagenesis in carbonates for temperatures below the clumped isotope blocking temperature

u pb dating of cements in mesozoic ammonites dating sedimentary carbonates using the u pb method can help improve the phanerozoic timescale using a novel combination of laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms and thermal ionization multi collector mass spectrometry tims u pb numerical ages were obtained on early diagenetic calcite cements in jurassic ammonites in which concentrations of u range from 0 47 to 5 3 ppm the calcite cements of two ammonites is1 and is2 from the uppermost bifrons zone of the toarcian 179 180ma of the uk gave tims normalized la u pb dates of 164 9 5 3 ma and 166 7 4 8ma respectively normalizing la icp mc ms data to an in house calcite standard gave a more precise date of 165 5 3 3 ma for is1 cement an unzoned ammonite ss2 of bajocian age 168 170 ma yield a tims normalized la u pb age of 158 8 4 3 ma for its early diagenetic cement both the combined la mc icp ms and tims approach and the use of a calcite laser ablation standard can result in accurate ages of cements with uncertainties of 2 3 2 the later however is more efficient and precise these u pb dates of cements are 10 to 20 myr younger than the numerical ages of the biostratigraphic intervals from which the ammonites derive the u pb dates are taken to represent the time at which the aragonite shell of the ammonite inverted to calcite and released its u to precipitate in a late diagenetic alteration of early diagenetic fringing cements concentrations of u and pb in a range of other pristine biogenic carbonateswere found too low u b 0 01 ppm for meaningful dating using laser ablation method

improving paleohydrological and diagenetic reconstructions in calcite veins and breccia of a sedimentary basin by combining δ47 temperature δ18owater and u pb age abstract in sedimentary basins the precise temperature and timing at which relatively shallow

a karst hydrology model for the geomorphic evolution of grand canyon arizona usa abstract the evolution of grand canyon started 85 ma when the southwestern hualapai plateau section of the colorado plateau began uplifting this uplift initiated a northeast trending drainage canyon system laramide paleo grand canyon that was to constrain all later routes including that of the colorado river this drainage proceeded down dip but up the stratigraphic section so that northward incision intersected progressively younger paleozoic to mesozoic rock we propose a capture of groundwater by the karstic redwall limestone at rm 197 that shifted the drainage direction of this early canyon along a n60 e trending section to rm 130 uplift of the kaibab arch at 80 65 ma forced coconino plateau drainage to divert around the west side of the arch rather than northeast across it in the mid tertiary an arizona river in the western grand canyon transported shinumo clasts to the california sespe formation and a magmatism tectonic volcanism episode occurred on and south of the hualapai plateau by 17 ma basin and range down faulting furthered earlier miocene canyon headward erosion eastward and then northward into utah causing a complete regional drainage reversal southward this miocene western paleo grand canyon river incised into the redwall muav karst aquifer so as to supply the 12 6 ma hualapai limestone with high 87sr 86sr carbonate spring water a 6 0 5 5 ma final connection between the east and west sides of the kaibab arch was accomplished by karst piracy drainage traversing under the arch this complexity of origin separate canyon sections joined drainage reversals and a final karst connection is why grand canyon remains enigmatic to geologists

u pb dating of calcite cement and diagenetic history in microporous carbonate reservoirs case of the urgonian limestone france microporous carbonates can constitute excellent hydrocarbon reservoirs if their micro pore and or nanopore structure is sufficiently developed and continuous in such deposits assessing the exact timing of reservoir property stabilization is critical to better understand the postdepositional processes favorable to the creation or preservation of porosity however placing reliable and accurate chronological constraints on the formation of microporosity in these reservoirs is a major challenge in this study we performed absolute u pb dating of calcite cements occurring in the urgonian microporous limestone northern tethys margin of southeastern france u pb ages ranging between 96 7 4 9 ma and 90 5 1 6 ma were obtained on the major calcitic phase responsible for the cementation and therefore the stabilization of microporosity indicating that this diagenetic process occurred synchronously at the regional scale following an extended subaerial exposure our results show that 1 the mineralogical stabilization process responsible for the formation of an excellent pervasive microporous network took place relatively early and 2 the so acquired reservoir quality was preserved for more than 90 m y these observations emphasize the importance of long exposure periods and associated meteoric influx for the formation and preservation of good microporous reservoirs

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits

the radiocarbon record in varved sediments of carmen basin gulf of california a measure of upwelling intensity variation during the past several hundred years the decrease in 14c 12c with depth in a varved sediment core raised from the eastern flank of carmen basin gulf of california is greater than expected from varve and 210pb chronology the discrepancy is ascribed to a virtually monotonic decrease in upwelling intensity from several hundred years ago to the present this radiochemical study presents an approach independent of previously used biostratigraphic techniques for evaluating temporal variations in upwelling intensity in the gulf of california

nitrate in groundwater and water sources used by riparian trees in an agricultural watershed a chemical and isotopic investigation in southern minnesota this study evaluates processes that affect nitrate concentrations in groundwater beneath riparian zones in an agricultural watershed nitrate pathways in the upper 2 m of groundwater were investigated beneath wooded and grass shrub riparian zones next to cultivated fields because trees can be important components of the overall nitrate pathway in wooded riparian zones water sources used by riparian trees and possible effects of trees on nitrate concentrations in groundwater were also investigated average nitrate concentrations in shallow groundwater beneath the cultivated fields were 5 5 mg l upgradient of the wooded riparian zone and 3 5 mg l upgradient of the grass shrub zone shallow groundwater beneath the fields passed through the riparian zones and discharged into streams that had average nitrate concentrations of 8 5 mg l as n lateral variations of d values in groundwater showed that mixing among different water sources occurred beneath the riparian zones in the wooded riparian zone nitrate concentrations in shallow groundwater were diluted by upwelling nitrate poor deep groundwater upwelling deep groundwater contained ammonium with a 15n of 5 that upon nitrification and mixing with nitrate in shallow groundwater caused nitrate 15n values in shallow groundwater to decrease by as much as 19 5 stream water penetrated laterally beneath the wooded riparian zone as far as 19 m from the stream s edge and beneath the grass shrub zone as far as 27 m from the stream s edge nitrate concentrations in shallow groundwater immediately upgradient of where it mixed with stream water averaged 0 4 mg l in the wooded riparian zone and 0 8 mg l near the grass shrub riparian zone nitrate concentrations increased toward the streams because of mixing with nitrate rich stream water because nitrate concentrations were larger in stream water than shallow groundwater concentrated nitrate in the streams cannot have come from shallow groundwater at these sites water sources of riparian trees were identified by comparing d values of sap water soil water groundwater and stream water soil water was the main water source for trees in the outer 4 to 6 m of one part of the wooded riparian zone and outer 10 m of another part groundwater was a significant water source for trees closer to the streams where the water table was less than about 2 1 to 2 7 m below the surface no evidence was found in the nitrate concentration profiles that trees close to the streams that took up groundwater through their roots also took up nitrate from groundwater the lack of such evidence is attributed to the nitrate concentration profiles being insufficiently sensitive indicators of nitrate removal by trees