travertine deposits of soda dam new mexico and their implications for the age and evolution of the valles caldera hydrothermal system uranium thorium disequilibrium dates and stable isotope analyses of travertine deposits at soda dam new mexico have been used to determine the age and to document the evolution of the valles caldera hydrothermal system soda dam discharges from paleozoic and precambrian rocks in san diego canyon southwest of the caldera and the canyon was filled with several hundred metres of upper bandelier tuff during formation of valles caldera 1 12 ma according to the dates the valles hydrothermal system is at least 106 yr old or nearly as old as the caldera the basic hydrology of the system has thus remained virtually unchanged during this time travertine ages indicate pulses in travertine deposition from 1 0 to 0 48 ma from 0 107 to 0 058 ma and from 0 005 ma to present the volume of various travertine deposits suggests that the hot spring system at soda dam was once larger than it is today possibly discharging as much as 5 to 10 times more fluid of na hco3 cl composition stable isotopes of the travertines indicate however that the hot spring system has probably never been more than about 10 c hotter than the present maximum temperature of 48 c stable isotopes also show that the 13c of co2 and 18o of h2o in hot spring waters has remained relatively constant for 106 yr the similar ages between caldera formation and the onset of large scale hydrothermal circulation and travertine deposition on pre bandelier tuff rocks imply that incision rates by the jemez river in bandelier tuff were relatively rapid as much as 400 m of tuff were cut by the ancestral jemez river in 105 yr or less

some considerations on the spectral features of meridional heat transport by transient eddies the present study analyses extreme events in meridional atmospheric heat transport due to transient eddies in the time frequency domain the data used are the european centre for medium range weather forecasts ecmwf era interim reanalysis data at the 850 mb pressure level and with daily 0 7 latitude and longitude resolution fast growing atmospheric modes are associated with large heat transport which would suggest a link between transport extremes and growing baroclinic systems defined here as motions in the 2 5 6 day band however by analyzing wavelet power spectra of transport extremes and of the corresponding meridional velocity and moist static energy temporal anomalies this is found not to be the case in fact baroclinic systems provide only a modest contribution to the integrated power of the extreme heat transport event spectrum the transport extremes are driven by very precise phase and coherence relationships between the velocity and moist static energy anomalies acting over a broad range of frequencies 2 5 30 days planetary scale motions k 0 4 with periods beyond 6 days play a key role in this framework

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

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

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

drill hole design for dilational ore shoot targets in fault fill veins ore along fault fill veins typically has an uneven distribution with semilinear high grade ore shoots separated by lower grade zones or barren fault segments therefore a successful drill campaign must be optimally designed for intersection of ore shoots and not the intervening zones however the typical drill hole design for fault fill veins which targets the vein directly downdip from the highest grade outcrops will miss most ore shoots that rake less than 80 to 90 in the structure dilational ore shoots form along pre or synmineralization faults in localized elongated structural openings perpendicular to the slip vector the rake of such ore shoots in fault fill veins can be predicted using models of stress controlled fault fracture kinematics equations are presented that use fault kinematic data to design drill holes for optimal success in targeting such ore shoots the equations calculate the universal transverse mercator utm coordinates of the drill target given fault fill vein orientation slip vector rake usually determined from slickenlines vertical depth to intersect the ore shoot and the utm coordinates of geochemically anomalous outcrops along the fault vein although the method assumes that fault kinematics control ore shoot orientation and is not applicable to all fault vein ore shoots such as those formed at intersections of faults or shear zones with permeable beds other faults or dikes the method increases the probability of success for drill testing ore shoots through optimal drill hole design

geochemical and palynological sea level proxies in hemipelagic sediments a critical assessment from the upper cretaceous of the czech republic geochemical and palynological records are presented for an expanded turonian coniacian hemipelagic succession in the central bohemian cretaceous basin a high resolution stratigraphic framework is provided by biostratigraphy and organic carbon stable isotope 13corg chemostratigraphy a short term 100 kyr sea level curve has been derived from high resolution transgressive regressive maxima shore proximity data established from basin wide sediment geometries the viability of geochemical and palynological parameters as potential sea level proxies is tested against this independently derived sea level record elemental chemostratigraphy is demonstrated to offer a reliable means of identifying medium to long term 0 4 2 4 myr sea level trends manganese maxima are associated with periods of high sea level and troughs with intervals of low sea level falling mn contents accompany regression and rising values transgression major transgressive events associated with medium term sea level change are marked by sharp increases in ti al ratios but short term 100 kyr sea level cycles are not consistently identified long term 13corg variation and dinoflagellate cyst species richness are positively correlated and show similarities to the sea level curve baseline trends have a cycle duration close to the 2 4 myr long eccentricity cycle dinocyst species richness closely follows short term changes in sea level with marked increases in dinocyst diversity coincident with most short term flooding events periods of rapid sea level rise caused an influx of a more diverse outer shelf assemblage into the study area together with the addition of shallower water species some of which may have been transported into the central basin by hypopycnal flows changes in the proportion and abundance of peridinioid dinoflagellate cysts principally palaeohystrichophora infusorioides were controlled principally by changing nutrient levels proximity proxies derived from geochemical and palynological data are not always consistent with the independent sea level model this exemplifies the need to understand all factors influencing elemental geochemical and palynological proxies before making simplistic sea level interpretations

depositional and organic carbon controlled regimes during the coniacian santonian event first results from the southern tethys egypt abstract geochemical and palynological proxies were determined for 31 samples representing the upper coniacian lowermost campanian abu roash a member collected from the bed2 3 well this was done to assess the prevailing paleoredox conditions productivity levels and water column settings to 1 understand controls and mechanisms related to accumulation of organic carbon within the sedimentary record 2 assess principal environmental processes that triggered the preservation of organic matter poor calcareous shale and limestone facies of the abo roash a member and 3 to interpret the paleoceanographic settings and confirm the occurrence of either oceanic anoxic event 3 oae3 or cretaceous oceanic red beds corbs within the abu gharadig basin in the southern part of the tethyan ocean egypt sedimentation rates were reconstructed based on the biostratigraphic age constraints of marine dinoflagellate cysts dinocysts trace elements based ratios and relationships were used in order to study the role of clastic terrestrial input three groups of dinocysts and freshwater pediastrum algae were used to study the water column conditions results showed that the abu roash a member was deposited under oxic to intermittently dysoxic conditions in a distal inner to middle neritic environment with varying sedimentation rates from 32 to 119 mm kyr 1 productivity appeared to be a significant factor for determining magnitudes of the organic carbon accumulation however low productivity was prevalent during deposition carbonate content was high which resulted in dilution of organic matter during varied rates of sediment input such results indicate that the paleoceanographic conditions in the southern tethys witnessed the absence of prevalent oceanic anoxia i e the coniacian santonian oae 3 and deposition of the corbs as in several parts of the tethys the pacific and the indian oceans

noble gas evidence for two fluids in the baca valles caldera geothermal reservoir noble gas elemental and isotopic abundances were measured in steam from four wells in the baca geothermal reservoir located in the valles caldera new mexico the 40ar36ar ratio and noble gas elemental abundances relative to 36ar are all strongly correlated with 1 36ar the inverse of the argon content ratios of n produced 21ne and radiogenic 40ar to total 4he dominantly radiogenic are nearly constant at 2 1 10 8 and 0 20 respectively the 3he4he ratio covers a restricted range of 3 9 to 4 8 times atmospheric the high 3he content of the gas indicates the presence of a helium component ultimately derived from the mantle kr and xe isotopic compositions are close to atmospheric excess 129xe is 0 25 of the total 129xe the high degree of linear correlation among the various noble gas results strongly suggests that the baca reservoir contains two distinct fluids that are produced in varying proportions from individual wells the noble gases in fluid a 2900 mg 1 c1 are air like but with lighter gases and isotopes preferentially enriched the fluid a 36ar content is low only 13 that of 10 c air saturated water asw the second fluid b 1700 mg 1 c1 is the dominant carrier of the radiogenic and mantle derived gases the heavier non radiogenic gases are preferentially enriched in fluid b and its 36ar content is very low only 5 7 asw the source of the noble gases in fluid a is tentatively ascribed to leaching of the relatively young 1 4 m y volcanic bandelier tuff the radiogenic gases and mantle derived helium in fluid b suggest a deeper source possibly including gases escaping from a magma

noble gases in formation fluids from deep sedimentary basins a review abstract atmospheric ne ar kr and xe are observed in fluids occurring in deep basins modifications of their abundance patterns reveal modes of recharge and brine formation phase separations during boiling and association of natural gas with water or oil radiogenic 4 he and 40 ar serve as age indicators of entrapped fluids effective over a significant portion of the geological time scale simultaneous application of 13 c atmospheric noble gases and radiogenic 4 he and 40 ar is recommended to identify a recent bacterial natural gas formation not accompanied by oil and b natural gas formed along with oil in a mature source rock

concepts and methods of high resolution event stratigraphy modern geological analyses involving sedimentary rocks require a high resolution system of dating integrating and correlating diverse strati graphic geochemical and paleontological data that also takes into account the possibility that short term phenomena 100 kyr or less exercise a strong control on sedimentation such phenomena may be extraterrestrial tectonic volcanic oceanographic climatic sedimentologic and or bio logic in origin some reflect unpredictable perturbations of local to global scale but most short term phenomena are predictable and may be either autocyclic locally regulated with limited stratigraphic continuity or allo cyclic in nature regionally to globally regulated with extensive strati graphic continuity beerbower 1964 a stratigraphic system based on short term phenomena would ideally be chronostratigraphic involving the identification and regional tracing of time lines isochronous surfaces or very thin event deposits and easily integrated with refined independently derived biostratigraphic and geochronologic systems an intensive search for such a new and revolutionary system of stratig raphy has been prompted in many parts of the phanerozoic by attain ment of plateaus in stratigraphic resolution utilizing the more standard tools of magnetostratigraphy biostratigraphy and geochronology most magnetic reversals have been identified biostratigraphic systems can be no more refined than the maximum evolutionary rates of component taxa and their major structures known for many favored groups and geo chronology is regulated by the analytical confidence limits of radiometric

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

brine history indicated by argon krypton chlorine bromine and iodine analyses of fluid inclusions from the mississippi valley type lead fluorite barite deposits at hansonburg new mexico argon krypton chlorine bromine and iodine were measured in a homogeneous population of high salinity hydrothermal fluid inclusions from the tertiary age mississippi valley type mvt lead fluorite barite deposits at hansonburg new mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts noble gases and halogens in fluid inclusions containing 10 10 10 9 l of brine cl 3 molal were analyzed by laser microprobe noble gas mass spectrometry lmngms on neutron irradiated samples the concentrations of36ar 4 7 10 8 molal and84kr1 8 10 9 molal in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately20 5 the mole ratios ofbr cl 1 2 10 4 andi cl 1 2 10 6 are among the lowest measured in any natural waters similar to those of modern brines formed by dissolution of permian nacl bearing evaporites in southeast new mexico 40ar 36ar ratios 600 are twice that of air and indicate that the fluid inclusions had excess radiogenic40ar 1 4 10 5 molal when trapped the amount of excess40ar appears to be too large to have been acquired with cl by congruent dissolution of halite bearing evaporites and possibly too small to have been acquired with pb by congruent dissolution of granitic basement rocks with proterozoic kar ages from thelmngms data combined with published pb and s isotope data we infer the following sequence of events in the history of the hansonburg mvt hydrothermal brine 1 the brine originated as relatively dilute meteoric water and it did not gain or lose atmospheric ar or kr after recharge 2 the originally dilute fluid acquired the bulk of its cl and sulfate in the subsurface after recharge by dissolving halite bearing permian marine evaporites 3 the high salinity brine then acquired most of its pb and excess radiogenic40ar from interactions with aquifer rocks other than evaporites possibly clastic sedimentary rocks or basement rocks with phanerozoic kar ages and 4 the brine deposited fluorite without having boiled or degassed

the use of cyclic stratigraphic pattern of peridinioid and gonyaulacoid dinoflagellate cysts in differentiating potential thick monotonous carbonate reservoirs a possible ecostratigraphic tool under test abstract the current work used the conventional peridinioid gonyaulacoid ratio p g to devise a new concept of dinoflagellate cyst zonation called the dinoflagellate ecological zone dez which is based here on the peridinioid ecological zone pez and gonyaulacoid ecological zone gez the pez and gez were used successfully to further divide the thick monotonous carbonate succession mid cenomanian to campanian in q 72 1x well in the eastern desert of egypt into smaller ecozones pez and gez are practical and easy to use in subdividing large conventional biozones of the carbonate reservoirs into distinguishable smaller ecozones when a finer resolution is necessary on a reservoir scale for production demands this tool is suggested to be used in the hydrocarbon exploration industry with minimum knowledge of the taxonomy of the dinoflagellate cysts the proposed pez and gez are related to local ecological conditions within the basin hydrocarbon field i e can be traced out laterally in an intra basinal scale this tool can be applied to any carbonate reservoirs in any petroliferous basin worldwide moreover the p g ratio the relative abundances of the dinoflagellate cyst assemblages and other palynological parameters were used successfully to reveal the palaeodepositional settings of the identified pez and gez alternating transgressive and regressive phases were identified although a dissimilar species composition is observed in each of these ecozones environments were interchanging between the regressive marginal marine to proximal inner neritic and the transgressive distal inner to middle shelf settings three peridiniacean dinoflagellate cyst peaks were recorded the middle cenomanian subtilisphaera peak the middle coniacian isabelidinium chatangiella and manumiella peak and the middle santonian isabelidinium peak

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

integrated sequence stratigraphy facies stable isotope and palynofacies analysis in a deeper epicontinental carbonate ramp late jurassic sw germany abstract sequence stratigraphy in deeper water epicontinental carbonates such as in the upper jurassic of southern germany is difficult because the recognition of parasequences sequences and sequence boundaries is impeded by the paucity in diagnostic sedimentological criteria or stratal surfaces using the genetic stratigraphic approach and integrating facies stable isotope c o and palynofacies analysis two types of genetic depositional sequences can be discriminated small scale sequences are stacked into medium scale sequences which may record a 400 kyr milankovitch signal the medium scale sequences were correlated regionally using both gamma ray logs and stable isotope records regional correlations show that the depocentres are controlled by underlying palaeotectonic elements late palaeozoic troughs the rise fall turnarounds of medium scale sequences are marked by negative 18o peaks temperature maxima and reduced absolute palynoclast contents the fall rise turnarounds are marked by positive 18o peaks temperature minima and high absolute palynoclast contents the initiation and termination of sponge microbial mounds show characteristic patterns thrombolitic microbialites form during intervals of 1 reduced input of terrestrial palynomorphs interpreted as an increase in distality 2 decreasing 13c trends interpreted to be related to decreasing nutrient supply and 3 decreasing 18o values interpreted as phases of warming and rising relative sea level in contrast thrombolitic stromatolitic microbialites were found to occur during phases of 1 increasing input of terrestrial palynomorphs interpreted as an increase in proximality 2 increasing 13c values interpreted to reflect increasing terrestrial input and nutrient supply as well as increasing 18o values interpreted as phases of cooling and relative sea level falls isotopic and palynofacies evidence suggests that bioherms were terminated by sudden input of nutrients during relative sea level falls sedimentological criteria were clearly not sufficient to delineate a robust sequence stratigraphic framework

the k pg boundary at brazos river texas usa an approach by marine palynology two cores and one outcrop section from the cretaceous palaeogen k pg boundary interval at the brazos river area texas usa have been high resolution sampled and analysed fully quantitatively by marine palynology the results have been compared and integrated with data from micropalaeontology sedimentology and isotope geochemistry from the same sections within all three sections the k pg boundary defined as the base of the p0 foraminifera zone and the onset of a negative carbon isotope anomaly closely corresponds to the appearance of lowermost danian organic walled dinocysts based on various palynological proxies as well as on sedimentologic features a sequence stratigraphic subdivision of the sections is proposed from a synopsis of all three sections a long term punctuated drop of relative sea level is indicated starting at about the top of the upper cretaceous cf2 foraminifera zone and reaching a minimum within the upper p1a zone of the lower palaeogene this is followed by a prominent transgression starting within the p1a p1b boundary interval the event deposit ed a siliciclastic unit located well below the base of the p0 foraminifera zone in the present sections most probably represents a combination of both episodic relative sea level fall and lag deposit due to initial transgression it is preceded by significant fluctuations of climatic boundary conditions with cool climates correlating to heavier 13c values and increased p g ratio of dinocysts suggestive of higher marine primary productivity across the k pg boundary a prominent increase and spike of the warm temperate waters dinocysts fraction is documented represented mainly by trithyrodinium evittii which is accompanied by climatic warming and an episodic relative sea level rise thus prominent paleo environmental changes and sea level fluctuations precede and coincide with the k pg boundary proper these data are inconsistent with a single catastrophic impact as the cause for the k pg boundary event but suggest relative longer term environmental stress as finally leading to end cretaceous crisis of the biosphere between the ed and the k pg boundary proper the gradual increase to peak abundance in trilete spores demonstrates a significant time lag between these two horizons according to the distinct distribution of this peak abundance it cannot be excluded that an impact tsunami event is related to the lower portion of the ed in contrast no significant changes within most palynologic proxies are documented across the yellow clay layer below the ed documented within one of the sections and recently suggested as the original chicxulub impact ejecta horizon this questions the impact origin of this horizon or at least suggests only little consequences of this event on the ecosystem

calcareous nannofossil paleoecology of the mid cretaceous western interior seaway and evidence of oligotrophic surface waters during oae2 abstract analysis of calcareous nannofossils total organic carbon toc values and carbon isotope records from outcrop and drill cores in the central colorado and kansas and southern texas western interior basin wib indicates predominantly oligotrophic surface water conditions during the late cenomanian turonian oceanic anoxic event 2 oae2 high resolution bio chemostratigraphy of this interval allows for detailed correlation of changes in nannofossil assemblages and toc across the wib and aids comparison with other global records prior to and at the onset of oae2 the a interval in the 13c positive excursion identified by pratt and threlkeld 1984 mesotrophic to eutrophic nannofossil taxa biscutum and zeugrhabdotus are relatively high in abundance and foraminiferal assemblages record a high diversity benthonic zone toc sharply declines at the start of oae2 despite evidence of high surface productivity and benthic diversity implying that the seafloor was briefly oxygenated during a period of enhanced mixing in the expanding western interior seaway during the latter two thirds of oae2 intervals b and c in the excursion toc periodically increases suggesting that anoxic conditions returned at the substrate despite persistently low abundances of biscutum and zeugrhabdotus implying oligotrophic surface water conditions the divergence of these two proxies suggests a highly stratified water column in the wib not higher productivity which resulted in anoxic conditions during oae2 if productivity was not the primary cause of increased carbon burial in the wib it is probable that increased terrestrial runoff and incursion of warm saline tethyan waters from the south led to salinity stratification in the absence of mixing warm and saline bottom waters would have been isolated from freshened boreal currents and become stagnant allowing for preservation of greater amounts of organic material in the substrate nannofossil records from cuba ks are an exception and reveal relatively high productivity throughout suggesting that occasional mixing of nutrients to the surface may have continued along the eastern margin of the central wib

dinoflagellate cysts paleoproductivity and upwelling systems a late cretaceous example from israel abstract diverse assemblages of dinoflagellate cysts occur in coniacian maastrichtian sedimentary sequences in israel which represent the inner shallower and outer deeper seaward belt of a late cretaceous upwelling system along the margin of the southern tethys the assemblages are composed mainly of peridinioid p and gonyaulacoid g cysts in varying concentrations it is suggested that the observed fluctuations in the numerical peridinioid gonyaulacoid p g cyst ratio reflect mainly changes in upwelling intensity and productivity in the studied area high p g values represent a higher productivity and vice versa thep g curve indicates a generally high productivity during the campanian followed by a decrease during the maastrichtian the inner part of the upwelling region is characterized by higherp g values representing a higher productivity the similarity between thep g ratio curve and the foraminiferal based paleoproductivity curve from the same sections supports the utility of thep g ratio as a reliable productivity indicator applied here for the first time to upper cretaceous sediments

helium accumulation in groundwater ii a model for the accumulation of the crustal 4he degassing flux abstract a model of 4 he accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4 he into the bottom of a confined aquifer the model is consistent with the measurements of 4 he concentration in the great artesian basin australia torgersen and clarke 1985 and also with the measurements of 4 he concentration in the auob sandstone of namibia heaton 1981 the measured value of the crustal degassing flux of 4 he from these two areas is comparable with the 4 he degassing flux calculated from the atmospheric budget of 4 he wasserburg et al 1963 ozima and podosek 1983 a literature review suggests that a crustal degassing 4 he source may account for the 4 he accumulation in many other groundwater systems it is concluded from the literature review the detailed modelling of 4 he accumulation in gab and the auob sandstone and the atmospheric budget that crustal degassing of 4 he may be a common and widespread phenomena

noble gases from honduras geothermal sites the elemental and isotopic composition of noble gases in hot springs and geothermal test wells were determined as part of a collaborative project to evaluate the potential for geothermal development in honduras central america the relative abundances of the noble gases in samples from the test wells indicate recharge temperatures for the geothermal systems equivalent to mean annual temperatures a common ratio of radiogenic 40ar to 4he of 0 35 corresponding to a k u ratio of 2 104 was found in samples from three of the studied areas platanares azacualpa and san ignacio a constant ratio may imply a common reservoir rock possibly the valle de angeles group of cretaceous to eocene age 3he 4he ratios are correlated in a positive sense with so4 concentration and in a negative sense with geothermal reservoir temperatures determined from chemical geothermometers these correlations are best explained by dilution of primary geothermal fluids with cooler sulfate rich waters the cooler waters inhibit deep boiling preserving high 3he 4he ratios in the surface springs in the el olivar region either the cool diluting fluid is sulfate poor or there is additional excess 3he provided by nearby quaternary trachytic to basaltic volcanism of the southern yojoa graben

temporal relations of volcanism and hydrothermal systems in two areas of the jemez volcanic field new mexico two hydrothermal alteration events 8 07 ma one sample 6 51 5 60 ma six samples related to the waning stages of late miocene volcanism ge 13 to le 5 8 ma are recognized at the cochiti district southeast jemez mountains most of the k ar dates 0 83 plus minus 0 11 0 66 plus minus 0 21 ma four samples in the hydrothermally altered caldera fill rocks of core hole vc 2a at sulfur springs valles caldera indicate post valles caldera hydrothermal alteration a sample from acid altered landslide debris of postcaldera tuffs from the upper 13 m of the core hole was too young to be dated by the k ar method and is possibly associated with current hot spring activity and the youngest pulses of volcanism oxygen isotope data from illite smectite clays in the cochiti district are zonally distributed and range from minus 2 15 per thousand to plus 7 97 per thousand smow depending upon temperature extent of rock fluid interaction and composition the samples from vc 2a get lighter with depth minus 0 20 per thousand to plus 1 62 per thousand the k ar and oxygen isotope data provide strong evidence that the epithermal quartz vein hosted gold silver mineralization at cochiti and the sub ore grade molybdenite at vc 2a were deposited in the late miocene 5 99 5 60 ma and mid quaternary approximately 0 66 ma respectively by hydrothermal fluids composed primarily of meteoric water

late aptian cretaceous paleoceanography of the south atlantic ocean inferred from dinocyst communities of the sergipe basin brazil the late aptian early cretaceous is a crucial time interval for understanding the paleoceanographic changes in the southern hemisphere oceanographic changes in the emerging south atlantic ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the muribeca and riachuelo formations of the sergipe basin in northeastern brazil the subtilisphaera community in the lower and middle parts of the section appears to be related to the subtilisphaera ecozone and suggests the onset of tethyan influence in the central south atlantic in a restricted to inner neritic environment the succeeding spiniferites community in the middle part of the section represents the first significant transgression probably of eustatic origin the cyclonephelium exochosphaeridium community in the upper part of the section appears to be related to an oceanic event characterized by intermittent dysoxic anoxic conditions the uppermost part of the section is dominated by the spiniferites community related to a progressive regional transgression and culminating in an open marine fully tethyan environment in the central part of the widening south atlantic

the tribag breccia pipes precambrian cu mo deposits batchawana bay ontario the tribag breccia pipes located near the eastern extremity of lake superior are associated with keweenawan felsic intrusions and have yielded a k ar age of 1 055 or 35 m y the pipes cut archean diabase and greenstones but in terms of regional setting exhibit a relationship to keweenawan rifting four major breccia pipes occur in the district three contain large tonnages of disseminated subeconomic cu and cu mo mineralization but only two have supported mining that production amounted to 16 000 metric tons of copper from relatively high grade ore associated with domal fractures within the two pipes the pipes contain mainly angular fragments of the surrounding metavolcanic and granitic country rocks and exhibit sharp contacts hydrothermal alteration within the pipes is restricted to the vicinity of fractures and orebodies but becomes more pervasive downward mineralization of the pipes can be divided into four periods each marked by somewhat distinctive mineral assemblages and ore fluid characteristics period 1 resulted in formation of disseminated chalcopyrite molybdenite sulfides associated with magnetite pyrite epidote and quartz fluid temperatures were up to 469 degrees c and salinities ranged up to 48 5 equiv wt percent nacl period 2 resulted in deposition of coarsely crystalline quartz and carbonates in the breccia matrices accompanied by lesser amounts of zeolites pyrite and chalcopyrite fluid temperatures were approximately 420 degrees to 330 degrees c and salinities ranged from 12 to 1 5 equiv wt percent nacl period 3 and 4 mineralization resulted in deposition of orebodies in fracture controlled sites principal sulfides in period 3 ores are chalcopyrite and pyrite these sulfides are massive in character and were deposited from fluids ranging from approximately 412 degrees to 291 degrees c and 14 to 5 equiv wt percent nacl salinity period 4 ores have a mineralogy similar to that of period 3 but in addition contain sphalerite and galena are of a disseminated nature and were deposited from fluids of approximately 363 degrees to approximately 250 degrees c and of 17 to 6 equiv wt percent nacl salinity estimates of pressure during the entire mineralization episode range from about 248 to 550 bars with pressure up to 1 kb at times during period 1 these estimates suggest a regime that mostly fluctuated between hydrostatic and lithostatic conditions at a depth close to 2 500 m but during period 1 pressures attained nearly twice lithostatic pressure analyses of the fluids in inclusions indicate mineralizing waters of two types period 1 3 and 4 waters were ca na brines some of which contained copper in concentrations of thousands of ppm period 2 fluids were na ca brines containing about 90 ppm cu analysis of fluid inclusion gases detected co 2 h 2 h 2 s he and ar from these data and thermodynamic considerations it can be demonstrated that h 2 s concentrations decreased through the paragenesis the f sub o 2 varied from below to above h 2 s hso super 4 equilibria in period 1 2 and 3 solutions which boiled and the ph remained between 4 2 to 5 1 limited stable isotope measurements suggest fluids of primarily magmatic origin three of the breccias are thought to be the result of collapse resulting from the creation of open space by alteration and solution of rock at depths of about 3 km by fluids streaming upward along faults the remaining breccia has features indicative of fracturing by fluid under high pressure tribag breccias are postulated to be the result of identical processes which have formed cu mo breccias in cordilleran settings the difference between subeconomic disseminated mineralization and the viable more concentrated mineralization in domal fractures appears to be related to the creation of open space and the higher cu content of the ore depositing fluids

n2 ar he compositions in fluid inclusions indicators of fluid source abstract a quadrupole mass spectrometer was used to measure bulk samples of conservative gas species n 2 ar and he in fluid inclusions from a variety of hydrothermal systems analyses of these tracer elements help determine 1 1 if gases extracted by bulk inclusion analyses can provide accurate measurement of n 2 ar he in active and fossil geothermal systems 2 2 if hydrothermal fluids associated with paleogeothermal systems in a continental setting follow n 2 ar he systematics similar to th the western pacific rim active geothermal systems specifically new zealand and 3 3 whether different deposit types systematically vary with regard to n 2 ar he the n 2 ar he ratios of fluid inclusion volatiles released from recently deposited minerals from the valles system are similar to those of present day valles thermal waters those inclusion samples from deep within the valles system below a regional aquitard increase in n 2 compositions for inclusions from the questa and copper flat porphyry deposits are n 2 rich similar to those of arc related volcanic gases whereas those from taylor creek sn deposit appear to be mixtures of magmatic and crustal components n 2 ar he ratios of the precambrian tribag deposit suggest a basalt source but significant levels of self generated he from u and th in the inclusion fluids are also possible inclusions from two epithermal deposits with low salinity inclusions have n 2 ar he ratios trending towards air saturated meteoric waters asw and those inclusions with higher salinities indicate minor to no asw component the n 2 ar he ratios in fresnillo and cochiti inclusions which have magmatic helium isotopic ratios indicate additions of magmatic gases to meteoric fluids inclusions from sediment hosted deposits that contain hydrocarbon bearing brines are he rich as are meteoric waters with a long residence time in the crust at relevant pressure temperature composition conditions henry s law constants of n 2 ar and he are similar and thus the relative amounts of these species trapped under boiling conditions will not vary appreciably from solubility controlled amounts in coexisting liquid furthermore there is no evidence of he loss or gain in inclusions by diffusion process data from the various systems that were examined indicate that fluid inclusion n 2 ar he compositions may be related to magmatic fluid sedimentary brine deep circulating meteoric fluid and shallow circulating meteoric fluid sources which we modified from those proposed by giggenbach 1986 relationships between the n 2 ar he tracer gases and other measurable quantities in fluid inclusions are indicated to be helpful in understanding fluid mixing processes in paleogeothermal systems

on the sporadic nature of meridional heat transport by transient eddies the present study analyses meridional atmospheric heat transport due to transient eddies in the european centre for medium range weather forecasts era interim reanalysis daily 0 7 latitude and longitude resolution data at the 850 mb pressure level are used probability density functions pdfs of meridional transient eddy heat transport display a near zero most likely value and a very large skewness which highlights the dominant role played by extreme events when considering zonal sections in both the northern and southern hemispheres events in the top five percentiles typically contribute to over half of the net poleward transport as a result of this sensitivity to extremes a large fraction of the heat transport by transient eddies at a given location and season is realised through randomly spaced bursts a few per season rather than through a continuum of events the predominance of extreme events can be explained by the favourable phase relationship between meridional velocity and moist static energy temporal anomalies this and the spatiotemporal characteristics of the events are compatible with eady type growing systems copyright 2012 royal meteorological society

the hydrothermal outflow plume of valles caldera new mexico and a comparison with other outflow plumes stratigraphic temperature gradient hydrogeochemical and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the valles caldera hydrothermal ouflow plume hydrologic data suggest that 25 50 of the discharge of the valles outflow is confined to the jemez fault zone which predates caldera formation thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the jemez fault zone up to 190 c km shallow heat flow above the hydrothermal plume is as high as 500 mw m 2 near core hole vc 1 jemez fault zone to 200 mw m 2 at fenton hill jemez plateau chemical and isotopic data indicate that two source reservoirs within the caldera redondo creek and sulphur springs reservoirs are parents to mixed fluids flowing in the hydrothermal plume however isotopic data borehole data basic geology and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing the valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits jemez fault zone that strike away from the source reservoir stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks the valles configuration is contrasted with the configuration of the hydrothermal plume at roosevelt hot springs which is dominated by lateral flow through a near surface widespread permeable aquifer data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings have varying reservoir compositions and have different flow characteristics although temperature reversals are commonly observed in wells penetrating outflow plumes reversals are not observed in all plumes less information is available on the absolute age of hydrothermal outflow plumes although the data show that they can be as old as 106 years and display episodic behavior

ore deposits at the fresnillo mine zacatecas mexico the fresnillo mine ore deposits consist of replacement chimney and manto bodies disseminated sulfide bodies and vein deposits hosted mainly in cretaceous marine sedimentary and volcanic rocks the base metal silver deposits are zoned to the southeast away from a small quartz monzonite stock with increasing silver content and decreasing base metal values with distance from the stock wall rocks adjacent to the stock exhibit silicification and calc silicate alteration that has been partially replaced by the sulfide minerals vein wall rocks exhibit potassic phyllic argillic and propylitic alteration with increasing distance from the veins chimney and manto bodies contain pyrite pyrrhotite sphalerite chalcopyrite galena tetrahedrite marcasite arsenopyrite and silver minerals chimney and manto bodies predate or are contemporaneous with base metal veins containing a similar mineralogy younger silver rich veins consist primarily of pyrargyrite with lesser acanthite proustite miargyrite polybasite tetrahedrite galena sphalerite and chalcopyrite individual veins exhibit increasing silver and decreasing base metal concentrations with increasing elevation fluid inclusions in quartz calcite and sphalerite contain two phases water and water vapor and are dilute 0 12 equiv wt nacl solutions filling temperatures and salinities vary sharply between growth zones in ore and gangue minerals with distinct salinity increases in sphalerite filling temperatures in chimney manto and deep vein quartz and calcite range between 240 degrees and 350 degrees c while shallow and distal quartz calcite and sphalerite from veins yield temperatures between 140 degrees and 275 degrees c sphalerite geobarometry of samples from the cueva santa manto yielded a total pressure of 730 bars pressure correction for the fluid inclusion filling temperatures from samples in chimney and manto deposits is 70 degrees c silverrich veins formed from fluids that were boiling indicating a depth of formation of 350 m below the paleosurface sulfur isotope analyses of galena and sphalerite from chimney manto and vein deposits exhibit overlapping ranges of values with galena depleted in 34 s with respect to sphalerite galena delta 34 s values from all deposit types at fresnillo vary between 4 1 and 8 0 per mil while sphalerite ranges between 2 0 and 5 0 per mil the calculated delta 34 s sub sigma s utilizing fluid inclusion filling temperatures is 3 0 or 0 4 per mil such a composition may have been derived from a slight shift in ore fluid ph as indicated by the wall rock alteration assemblages or by increased log f sub o 2 as indicated by minor hematite and amethystinc quartz from an original delta 34 s sub sigma s of 0 per mil galena lead isotope data indicate that mantos and veins formed from the same deep crustal source the fluctuating temperature and salinity values from growth zones in ore and gangue minerals deep crustal source of the lead and magmatic origin of the sulfur argue for a mineralizing system that derived its fluids from magmatic and meteoric sources the magmatic fluids associated with the quartz monzonite stock spread upward and outward along major regional faults and bedding planes of the sedimentary rocks mixing and cooling with meteoric fluids the ore and gangue minerals may have been precipitated due to mixing of these two fluids boiling of ore fluids may have caused ore mineral precipitation in the silver rich veins as suggested by sharp vertical increase in silver concentrations at the 350 m below the present surface level

helium isotopes in geothermal and volcanic gases of the western united states ii long valley caldera abstract systematic trends in helium isotope ratios and gas compositions in long valley caldera hot spring and fumarole gases reflect subsurface processes and conditions in the hydrothermal system high 3 he 4 he ratios to 6 5 atmospheric indicate a magmatic helium source diluted to varying degrees by crustal radiogenic helium as observed in western united states geothermal systems in general helium isotope ratios increase eastward across the caldera which we interpret as an input of magmatic helium to the hydrothermal fluid as it flows eastward over the caldera decreasing he condensible gas he co2 ratios accompanying this trend suggest that co2 addition and or preferential helium loss due to boiling are also occurring although near surface ph related co2 hco3 equilibria obscure the nature of this effect substantial changes in 3 he 4 he ratios were observed in long valley gases between 1978 and 1985 helium isotope ratios increased by 15 in the hot creek thermal vent with maximum ratios achieved in 1983 helium isotope ratios subsequently decreased in this and other hot vents in the caldera these observations indicate that substantial changes in the mixing ratio of radiogenic and magmatic helium may occur over relatively short periods of time in magmatically active systems

fluid sources for the la guitarra epithermal deposit temascaltepec district mexico volatile and helium isotope analyses in fluid inclusions the la guitarra deposit temascaltepec district south central mexico belongs to the low intermediate sulfidation epithermal type has a polymetallic character although it is currently being mined for ag and au the mineralization shows a polyphasic character and formed through several stages and sub stages named i iia iib iic iid and iii the previous structural mineralogical fluid inclusion and stable isotope studies were used to constrain the selection of samples for volatile and helium isotope analyses portrayed in this study the n2 ar overall range obtained from analytical runs on fluid inclusion volatiles by means of quadrupole mass spectrometry qms is 0 to 2526 and it ranges 0 to 2526 for stage i 0 to 1264 for stage iia 0 to 1369 for stage iib 11 to 2401 for stage iic 19 to 324 for stage iid and 0 to 2526 for stage iii these values combined with the co2 ch4 ratios and n2 he ar and n2 ch4 ar relationships suggest the occurrence of fluids from magmatic crustal and shallow meteoric sources in the forming epithermal vein deposit the helium isotope analyses obtained by means of noble gas mass spectrometry display r ra average values between 0 5 and 2 pointing to the occurrence of mantle derived helium that was relatively diluted or contaminated by crustal helium these volatile analyses when correlated with the stable isotope data from previous works and he isotope data show the same distribution of data concerning sources for mineralizing fluids especially those corresponding to magmatic and crustal sources thus the overall geochemical data from mineralizing fluids are revealed as intrinsically consistent when compared to each other the three main sources for mineralizing fluids magmatic and both deep and shallow meteoric fluids are accountable at any scale from stages of mineralization down to specific mineral associations the volatile and helium isotope data obtained in this paper suggest that the precious metal bearing mineral associations formed after hydrothermal pulses of predominantly oxidized

reservoir processes and fluid origins in the baca geothermal system valles caldera new mexico at the baca geothermal field in the valles caldera new mexico 19 deep wells were drilled in an attempt to develop a 50 mwe megawatts electric power plant the chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes two distinct reservoir fluids exist at baca these fluids originate from the same deep high temperature 335 c saline 2500 mg kg cl parent water but have had different histories during upflow one fluid from wells 4 and 13 is isotopically light high in radiogenic noble gases co2 and hco3 and low in ca it has a temperature of 290 295 c and a reservoir chloride near 1900 mg kg this fluid resulted from rapid upward flow through 1 1 to 1 4 m y old bandelier tuff reservoir rocks after long residence in pre bandelier 7 m y sediments and precambrian basement rocks and 25 dilution with high altitude cold groundwater from redondo peak the other water from wells 15 19 and 24 moved slowly through the bandelier tuff and cooled conductively with minor steam loss for well 19 from 335 c to 280 260 c apparently short residence in old basement rocks has left this water with low radiogenic gases conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water the recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the valles caldera area gases are in equilibrium in all liquid reservoir fluids at near reservoir temperatures and the concentrations of atmospheric gases are similar to those of air saturated water indicating little boiling and steam loss all water solutes and gases in the reservoir fluids originate from air saturated meteoric recharge water watermineral reactions and rock leaching with the possible exception of excess 3he that must have an ultimate mantle source this gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the bandelier

hydrologic implications of alteration and fluid inclusion studies in the fresnillo district mexico evidence for a brine reservoir and a descending water table during the formation of hydrothermal ag pb zn orebodies ag pb zn mineralization in the fresnillo district formed from a large magma related hydrothermal system between approximately 32 to 28 ma a partial record of this hydrothermal activity is preserved by hydrothermal alteration mineral assemblages and fluid inclusions occurring in barren and mineralized parts of the district these features provide constraints on the hydrologic interpretation of the mineralizing system surficial exposures contain alteration assemblages which reflect two distinct fluid types that are known to occur in the shallow parts of active hydrothermal systems the hydrothermal mineral assemblage comprising quartz calcite illite or interlayered illite montmorillonite plus or minus chlorite pyrite or adularia occurs in scattered exposures around the district and indicates the former widespread presence of near neutral ph chloride waters fluid inclusion data in barren exposures south of the district center indicate that these fluids were dilute containing less than 5 wt percent nacl equiv and had temperatures in the range of 160 degrees to 240 degrees c the assemblage of kaolinite plus or minus alunite and natroalunite occurs locally above blind orebodies in the southern part of the district and in outlying exposures and indicates the former presence of acid sulfate waters geologic and fluid inclusion evidence strongly suggests that these waters originated as steam heated condensates which formed above the water table at plateros which lies north of fresnillo a hotter thermal environment is exposed where fluid inclusion data range from 220 degrees to 300 degrees c in contrast to other surficial exposures in the fresnillo district those that crop out in the center of the district on cerro proano contain significant silver mineralization associated with stockwork quartz veins fluid inclusion data from two quartz crystals indicate part of a complex hydrothermal history in which fluids of 17 10 and 200 degrees c this last feature explains why the tops of late formed orebodies are concealed at 150 to 200 m depth this model implies that dilute hydrothermal fluids devoid of ore metals were the fluids mostly responsible for hydrothermal alteration and vein fillings at the present day surface and that changes to the hydrology significantly altered the position of the ore depositional environment

an important source of4he and3he in diamonds a large data base has recently accumulated on the concentrations of helium isotopes in diamonds mined from various regions it was noted earlier ozima et al 1985 1 lal et al 1989 2 that the frequency distribution of the4he concentrations is a fairly narrow one whereas that of3he concentrations is a broad one with no pronounced peaks the ratios 3he 4he on the other hand show a broad maximum around 2 ra ra equals atmospheric 3he 4he ratio 1 40 10 6 with a slow decrease over two orders of magnitude on either side does this imply that the diamonds sample a wide variety of helium reservoirs having a range of 3he 4he ratios but somehow attain similar4he concentrations we propose that in a majority of the diamonds studied 4he is primarily due to implantation of radiogenic alpha particles from the host material after emplacement in the crust usually kimberlite and that the concentrations of4he in diamonds often get appreciably altered by this process thus the4he trapped in the diamond at the time of its crystallization is usually overwhelmed by the implanted helium and the measured 3he 4he ratios do not generally correspond to any sources in the mantle however the implanted4he resides in the outer 16 m of the diamond and the intrinsic4he and 3he 4he ratios in the diamond can be studied if its outer layers are removed the wider implications of diamond being the target material for nuclear reaction products from the host material are discussed radiogenic3he produced in the host material is also implanted in the diamond but this contribution is small on a gross basis however since the depth of implantation of3he is greater than that of4he some of the very high 3he 4he ratios observed in diamonds could be due to the implantation of radiogenic3he the radiogenic reactions in the host material can also contribute to appreciable21ne in diamonds

climatic cyclicity and terrigenous sediment influx to the early turonian greenhorn sea southern utah abstract rhythmically alternating beds of limestone and shale in pelagic deposits of the cenomanian turonian north american western interior seaway have been widely attributed to climatic cyclicity in the milankovitch band whether these rhythmic beds record cycles of terrigenous dilution or of productivity remains controversial we present results of a study of early turonian strata of the tropic shale and tununk member of the mancos shale in southern utah aimed at testing the dilution model in a prodeltaic environment within 130 km of the paleoshoreline the study transect consisted of four localities spaced along a 110 km onshore offshore transect in each of the four sections we studied a stratigraphic interval characterized by beds of limestone or marlstone that alternate with beds of marly shale or calcareous shale along the transect content of quartz sand and coarse silt in each of the beds generally decreases and content of calcium carbonate increases in each section quartz sand and coarse silt content varies antithetically with calcium carbonate content these observations suggest that the limestone marlstone beds accumulated during times when rates of terrigenous sediment transport to offshore sites were relatively slow conversely the shaly beds were deposited during times of enhanced terrigenous sediment flux these ob ervations support the hypothesis that limestone shale bedding rhythms record wet and dry phases of climate cycles in utah the limestone marlstone beds contain smaller proportions of mixed layer illite smectite clays than do the shaly beds climatic cyclicity apparently led to cyclic variations in the proportions of clay minerals supplied to the prodeltaic environments or to variation in the loci of accumulation of different clay minerals analysis of intensity of bioturbation and preservation of fecal pellets also indicates that the limestone marlstone beds accumulated under more oxic benthic conditions than did the shaly beds detailed examination of the alternating beds of limestone marlstone and shale in southern utah indicates that the deposits are characterized by a distinctive succession of facies these deposits are better interpreted as bedding cycles composed of three gradational lithologies than as bedding rhythms composed of two alternating lithologies data on grain size and calcium carbonate content suggest that the bedding cycles correspond to shoaling upward parasequences that developed in response to small scale changes in relative sea level our study suggests that climatically modulated changes in fresh water discharge and terrigenous sediment supply were mainly responsible for these sea level changes and for cyclic variations in benthic oxygenation in prodeltaic environments of the earl turonian western interior seaway

origin of the cretaceous bridge creek cycles in the western interior united states abstract alternating beds of burrowed limestone and laminated organic carbon rich marlstone in the bridge creek member of the greenhorn formation were deposited during maximum transgression of the cenomanian turonian sea in the western interior of the united states one view of the origin of the bridge creek limestone marlstone rhythms holds that they represent dilution cycles produced by alternating climates within the western interior the marlstones recording wet episodes when high runoff produced a sediment laden brackish lid on the seaway and the limestones recording dry episodes when runoff was low and the water column well mixed a second view holds that the rhythms represent productivity cycles the limestones representing times of high productivity of calcareous planktonic skeletons and the marlstones representing times of low productivity in this view the rhythms were produced by alternations in vertical circulation that characterized much of the world ocean at the time the productivity origin of the rhythms is supported by the presence of abundant calcispheres in the limestone beds the concentration of clay size quartz in many of the limestone beds the comparatively high 18 o and low 13 c in limestone beds the similarity in proportion of clay minerals in marlstone and limestone beds the pelagic depositional rate of the bridge creek member and by the discovery that bridge creek deposition began with a marlstone and not a limestone bed the dilution model is not consistent with these features and it has not been supported by modeling of paleoclimates and lithofacies that were predicted from it nor by macrofaunal distributions within the seaway the dilution model is not consistent with the occurrence of diverse and abundant planktonic foraminifera in both marlstone and limestone beds which indicate that near normal marine salinities prevailed during deposition of both bed by bed analysis of the bridge creek member may provide an analog for events in the tethys that are poorly recorded in deposits from the deep sea itself

calcareous nannofossil paleoceanography of the cretaceous greenhorn sea two distinctive laterally traceable bentonite beds were used to construct three isochronous time slices through the marine sediments of the upper cretaceous greenhorn cyclothem of the western interior basin calcareous nannofossil assemblages from these time slices were analyzed from 40 localities to examine the paleoceanographic conditions in the basin deposition of the lower time slice x bentonite approximately corresponded to the time at which free communication between the basin and open oceanic systems first occurred the most striking trend is the presence of common to abundant nannofossils in the center of the basin and their absence from the eastern and western margins this indicates that open oceanic conditions conducive to large standing crops of calcareous nannoplankton existed only in a narrow centrally located channel conditions at the basin margins were probably unsuitable for large populations due to salinity constraints multivariate analyses indicate two distinct biofacies northern and southern which are interpreted to represent distinct surface water masses the geometry of the water mass boundary suggests that the northern surface water mass actively flowed southward into or over the relatively passive southern water mass the upper time slice hl 3 bentonite samples the nannofossil distributions at or near the maximum transgression of the greenhorn sea in this time slice nannofossils occur beyond the limits of the study area except in proximity to the frontier delta system diversities are significantly higher indicating water mass conditions more similar to those in open oceanic settings multivariate analyses indicate three distinct surface water masses northern southern and western the northern and southern water masses exhibit relationships similar to those during the x bentonite time slices the interaction between the northern and southern water masses promoted vertical stratification of the water column and resultant sediment anoxia the western biofacies may be indicative of a surface water mass with significant contributions from nearby fresh water influx

fluid chemistry and evolution of hydrothermal fluids in an archaean transcrustal fault zone network the case of the cadillac tectonic zone abitibi greenstone belt canada detailed fluid geochemistry studies on hydrothermal quartz veins from the rouyn noranda and val d or areas along the transcrustal cadillac tectonic zone ctz indicate that unmineralized with respect to gold sections of the ctz contained a distinct co2 dominated h2s poor hydrothermal fluid in contrast both gold mineralized sections of the ctz e g at orenada 2 and associated higher order shear zones have a h2o co2 c h 4 nacl hydrothermal fluid their co2 h2s ratios indicate h2s rich compositions the br cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust oxygen isotope ratios from hydrothermal quartz veins in the ctz are consistently 2 more enriched than those of associated higher order shear zones which are inter preted to be a function of greater fluid rock ratios in the ctz and lower fluid rock ratios and more efficient equilibration of the hydrothermal fluid with the wall rock in higher order shear zones an implication from this study is that the lower metal endowment of the transcrustal ctz when compared with the higher metal endowment in higher order shear zones ratio of about 1 1000 may be the result of the lack of significant amounts of h 2o h2 sr ich fluids in most of the ctz in contrast gold mineralization in the higher order shear zones appear to be controlled by the high h 2s activity of the aqueous fluids because gold was likely transported in a bisulfide complex and was deposited during sulfidation reac tions in the wall rock and phase separation in the quartz veins

the sedimentological evolution and petroleum potential of a very thick upper cretaceous marine mudstone succession from the southern high latitudes a case study from the bight basin australia abstract during iodp expedition 369 a 690 m thick succession of silty claystone spanning the early turonian to the late santonian was encountered at site u1512 in the bight basin offshore southern australia stacking patterns sedimentary facies and palynological assemblages reveal that the succession was rapidly deposited with hyperpycnal and hypopycnal flows in a marine prodelta setting which was subject to basin restriction the dominance of clay rich facies and phytoclasts in the succession was likely the result of a major river system delivering a high sediment load into the bight basin when a warm wet climate prevailed a combination of high sedimentation rates 19 272 m myr and accelerated subsidence prevented the delta from rapidly prograding into more distal regions of the basin the complete turonian to santonian mudstone succession yields low total organic carbon 1 wt and type iv kerogens however palynofacies assemblages become progressively marine in character and total organic carbon values vary between 1 and 1 5 wt with depth this may indicate that the base of the hole at site u1512 was close to potential organic rich black shales associated with ocean anoxic event 2 low amplitude and irregular reflections on seismic data and disparities between biostratigraphic zonations suggest the upper 350 m of the turonian to santonian succession may represent a mass movement that happened during the pleistocene this study reveals that site u1512 material likely represents a near stratigraphically complete marine mudstone succession from high paleolatitudes as well as the only depositional record that was fully cored from the bight basin

coupled manganese and carbon isotopic events in marine carbonates at the cenomanian turonian boundary abstract the boundary interval between the cenomanian and turonian stages of the upper cretaceous shows a positive excursion in the carbon isotopic composition of organic matter and carbonate in many epicontinental and oceanic sections of the atlantic tethyan realm some of the studied epicontinental sections contain an excursion in the manganese content of carbonates coincident with the shift in carbon isotopic values in a key reference section at pueblo colorado the stratigraphic position and magnitude of the manganese excursion are described with respect to the carbon isotopic excursion coincident excursions in manganese contents and carbon isotopic values are verified for a section in normandy france the depositional setting for these two sections is persistently to intermittently we l oxygenated with the accumulation of interbedded chalky and marly sediments no shift in manganese values was detected through the isotopic excursion in a section from northern nebraska where fossils are preserved only as bedding plane impressions due to extensive early diagenetic dissolution of carbonate the carbon isotopic and manganese excursions begin at the same stratigraphic position but manganese contents return to background values within the lower half of the carbon isotopic excursion the relative timing and duration of these signals suggest the existence of a large manganese reservoir that was rapidly mobilized transfer of manganese from deep sea oxides mn4 to epicontinental carbonates mn2 is inferred to have occurred during expansion of oceanic oxygen minimum zones with associated changes in redox gradients and boundaries simultaneous excursions in carbon isotopic values and manganese contents can occur at sites of carbonate accumulation when the carbon and manganese cycles are linked through the reducing potential of widespread oxygen deplete water masses

meridional transport of eddy sensible heat in winters marked by extremes of the north atlantic oscillation 1948 49 1979 80 abstract composite patterns of eddy sensible heat transport at 700 mb on the northern hemisphere are derived for winters december january february djf marked by extremes of the north atlantic oscillation nao occurring in the 1948 49 1979 80 period statistically significant heat flux differences between the two nao modes ga greenland above gb greenland below normal temperatures relative to northern europe occur dominantly in the north atlantic sector these are connected to marked reversals in sea level pressure slp and an out of phase behavior of the zonal component of the geostrophic wind related to changes in the amplitude of wavenumber 2 teleconnections of the nao in terms of both pressure and eddy heat transport to the north pacific and east asian regions are found to be weak for those extreme events occurring since 1948 49 partitioning the total meridional heat flux into its transient and quasi stationary components confirms the dominance of the latter for the hemisphere as a who

meteoric interaction with magmatic discharges in japan and the significance for mineralization the andesitic volcanoes kirishima kyushu and esan hokkaido discharge 94 to 225 c hcl bearing vapors from summit fumaroles at kirishima a geothermal system exists on the flanks of the large volcanic massif 1500 m relief and 12 km radius in contrast esan is a small dome 600 m relief and 1 km radius with ephemeral hot springs the chemical and isotopic compositions of the fumarole gases and condensates and of waters from hot springs indicate that esan discharges are dominated by magmatic water and gases whereas those at kirishima are mainly meteoric the kirishima geothermal system contains acid fluids that are neutralized by interaction with the host rock and dilution by meteoric ground water the acidity is probably of magmatic origin a large ground water carapace at kirishima condenses a majority of magmatic volatiles and metals before they can discharge to the surface in contrast to esan where the volatiles including metals degas to the atmosphere this suggests that a meteoric system may be necessary to condense metals in this high level volcanic environment to provide a situation conducive to hydrothermal mineralization at epithermal depths

timing of magmatic activity and mineralization and evidence of a long lived hydrothermal system in the fresnillo silver district mexico constraints from 40ar 39ar geochronology the ore deposits of fresnillo have produced silver for more than 450 years and contain resources of approximately 1 goz mineralization in fresnillo occurs in epithermal veins hosted by a middle jurassic to late cretaceous volcanosedimentary sequence guerrero terrane late paleocene conglomerates and eocene to oligocene tuffs and flows of trachyte rhyolite and rhyodacite lie unconformably on top of the guerrero terrane steam heated acid sulfate alteration containing alunite veins occurs in eocene tuffs above some of the mineralized veins oligocene rhyolitic domes and a quartz monzonite stock also occur in the area whereas sporadic miocene basaltic flows and dikes are the youngest igneous rocks in the district spatial association of tertiary volcanic rocks intrusions acid sulfate alteration and epithermal veins makes the district ideal for evaluating the temporal relations between magmatism and hydrothermal activity using precise 40ar 39ar geochronology sanidine single crystal laser fusion analyses reveal discrete volcanic eruptions at 44 73 0 04 40 92 0 04 40 83 0 04 31 55 0 03 and 31 04 0 05 ma dating of orthoclase from the fortuna quartz monzonite was problematic due to excess argon contamination but a preferred age of 32 65 0 05 ma is suggested two adularia samples from the jarillas vein give statistically identical ages of 29 75 0 12 and 29 68 0 10 ma adularia from valdecanas vein shows a climbing age spectrum related to hydrothermal alteration however a terminal step with an age of 29 74 0 07 ma suggests that the two veins may be coeval alunite recorded two distinct ages at 30 56 0 04 and 31 03 0 05 ma alunite and adularia ages suggest that acid sulfate alteration and mineralization occurred separately well after emplacement of the dated phase of the fortuna stock and consequently it cannot be the source of heat for the hydrothermal system that formed those finally the 3 m y difference in age between epithermal mineralization and the fortuna stock is indicative of a long lived but episodic hydrothermal system which could have been driven by multiple pulses of small and shallow intrusions