Application of a Bayesian model to infer the contribution of coalbed natural gas produced water to the Powder River,Wyoming and Montana

The Powder River Basin (PRB) of Wyoming and Montana contains significant coal and coal bed natural gas (CBNG) resources. CBNG extraction requires the production of large volumes of water, much of which is discharged into existing drainages. Compared to surface waters, the CBNG produced water is high in sodium relative to calcium and magnesium, elevating the sodium adsorption ratio (SAR). To mitigate the possible impact this produced water may have on the quality of surface water used for irrigation, the State of Montana passed water anti‐degradation legislation, which could affect CBNG production in Wyoming. In this study, we sought to determine the proportion of CBNG produced water discharged to tributaries that reaches the Powder River by implementing a four end‐member mixing model within a Bayesian statistical framework. The model accounts for the ⁸⁷Sr/⁸⁶Sr, δ¹³C_DIC, [Sr] and [DIC] of CBNG produced water and surface water interacting with the three primary lithologies exposed in the PRB. The model estimates the relative contribution of the end members to the river water, while incorporating uncertainty associated with measurement and process error. Model results confirm that both of the tributaries associated with high CBNG activity are mostly composed of CBNG produced water (70–100%). The model indicates that up to 50% of the Powder River is composed of CBNG produced water downstream from the CBNG tributaries, decreasing with distance by dilution from non‐CBNG impacted tributaries from the point sources to ~10–20% at the Montana border. This amount of CBNG produced water does not significantly affect the SAR or electrical conductivity of the Powder River in Montana. Copyright © 2013 John Wiley & Sons, Ltd.     

The biogenic origin of needle fibre calcite

Needle fibre calcite is one of the most ubiquitous habits of calcite in vadose environments (caves deposits, soil pores, etc.). Its origin, either through inorganic, indirect or direct biological processes, has long been debated. In this study, investigations at 11 sites in Europe, Africa and Central America support arguments for its biogenic origin. The wide range of needle morphologies is the result of a gradual evolution of the simplest type, a rod. This rod is the elementary brick which, by aggregation and welding, builds more complex needles. The absence of cross‐welded needles implies that they are welded in a mould, or under a longitudinal and unidirectional constraint, before being released inside the soil pores. The difference between the lengthening of the needles and the c axis can be explained by the existence of needles observed under a scanning electron microscope in organic sleeves, which can act as a mould during rod growth. Complex morphologies with epitaxial outgrowths on straight rods cannot have grown entirely inside organic microtubes; they must result from soil diagenesis after the release of straight rods in a soil‐free medium. Whisker crystals are interpreted as the result of growth and coalescence of euhedral crystals on a rod. Rhomb chains are considered to be the consequence of successive epitaxial growth steps on a needle during variations in growth conditions. Isotopic signatures for needle fibre calcite vary from ?16·63‰ to +1·10‰ and from ?8·63‰ to ?2·25‰ for δ¹³C and δ¹⁸O, respectively. The absence of high δ¹⁸O values for needle fibre calcite precludes a purely physicochemical origin (evaporative) for this particular habit of calcite. As epitaxial growth cannot precipitate in the same conditions as initial needles, needle fibre calcite stable isotopic signatures should be used with caution as a proxy for palaeoenvironmental reconstructions. In addition, it is suggested that the term needle fibre calcite should be kept for the original biogenic form. The other habit should be referred to as epitaxial forms of needle fibre calcite.     

Late-glacial climatic oscillations as recorded in Swiss lake sediments

Regional pollen assemblage zones for the late-glacial period of the Swiss Plateau are introduced and defined. They include four major zones (Artemisia, Juniperus—Hippophaë, Betula, Pinus PAZ) with several subzones. Pollen and oxygen-isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000-9500 yr BP. The first oscillation, termed the Aegelsee fluctuation, occurs shortly before 12 000 yr BP and varve counts suggest its duration was ca. 100 yr. It is characterised by a short decrease in the oxygen isotopes as well as a short increase in NAP associated with a depression in birch pollen values. The second oscillation, which occurs in the δ¹⁸O record shortly before the deposition of the Laacher See Tephra (ca. 11 000 yr BP), is termed the Gerzensee fluctuation. It occurs during a pine-dominated phase and its vegetational effects cannot be determined palynologically. The most prominent regressive phase is the Younger Dryas biozone (ca. 10 700-10 000 yr BP) characterised by an increase in heliophilous NAP and low δ¹⁸O values. The Younger Dryas biozone can often be subdivided palynologically into two parts: a first part rich in grasses and juniper and a second part with higher Filipendula and birch values. During the Preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios. Comparison of the Swiss oxygen isotope profiles with the Greenland Dye 3 record suggests that not only the three major shifts in the δ¹⁸O curves but also the minor ones are closely comparable, suggesting some common climatic control.     

试用“稳定流”评价区域化探异常

出露地表或近地表的矿体,在遭受风化剥蚀作用时,稳定地向水系补充矿化物质,形成在矿体附近具有浓集中心,含量向下游逐渐衰减的水系沉积物异常,对这种异常的形成作用称之为“稳定流”。应用这一概念,可以筛选化探异常。进一步根据“稳定流”的长度和强度,还能够近似定量地推断未知矿化区面金属量(Ps)以及建立典型矿床水系沉积物元素分带序列,为寻找隐伏矿体,评价区域化探异常提供了一种新的方法。     

Isotopic constraints on fluid infiltration from an eclogite facies shear zone, Holsenøy, Norway

Granulite facies anorthosites on Holsenøy Island in the Bergen Arcs region of western Norway are transected by shear zones 0.1–100 m wide characterized by eclogite facies assemblages. Eclogite formation is related to influx of fluid along the shears at temperatures of c. 700d?C and pressures in excess of 1.7 GPa. Combined carbon and nitrogen stable isotope, ⁴⁰Ar/³⁶Ar, trace-element and petrological data have been used to determine the nature and distribution of fluids across the anorthosite-eclogite transition. A metre-wide drilled section traverses the eclogitic centre of the shear into undeformed granulite facies garnet-clinopyroxene anorthosite. Clinozoisite occurs along grain boundaries and microcracks in undeformed anorthosite up to 1 m from the centre of the shear and clinozoisite increases in abundance as the edge of the shear zone is approached. The eclogite-granulite transition, marked by the appearance of sodic pyroxene and loss of albite, occurs within the most highly sheared section of the traverse. The jadeite-in reaction coincides with increased paragonite activity in mica. The separation between paragonite and clinozoisite reaction fronts can be semiquantitatively modelled assuming advective fluid flow perpendicular to the shear zone. The inner section of the traverse (0.25 m wide) is marked by retrogressive replacement of omphacite by plagioclase + paragonite accompanied by veins of quartz-phengite-plagioclase. C-N-Ar characteristics of fluid inclusions in garnet show that fluids associated with precursor granulite, eclogite and retrogressed eclogite are isotopically distinct. The granulite-eclogite transition coincides with a marked change in CO₂ abundance and δ¹³C (<36ppm, δ¹³C=-2% in the granulite; <180 ppm, δ¹³C=-10% in the eclogite). The distribution of Ar indicates mixing between influxed fluid (⁴⁰Ar/³⁶Ar > 25 times 10³) and pre-existing Ar in the granulite (⁴⁰Ar/³⁶Ar < 8 times 10³). δ¹⁵N values decrease from +6% in the anorthosite to +3% within the eclogite shear. The central zone of retrogressed eclogite post-dates shearing and is characterised by substantial enrichment of Si, K, Ba and Rb. Fluids are CO₂-rich (δ¹³C ～ -5%) with variable N₂ and Ar abundances and isotopic compositions. Both Ar and H₂O have penetrated the underformed granulite fabric more than 0.5m beyond the granulite/eclogite transition during eclogite formation. Argon isotopes show a mixing profile consistent with diffusion through an interconnecting H₂O-rich fluid network. In contrast, a carbon-isotope front coincides with the deformation boundary layer, indicating that the underformed anorthosite was impervious to CO₂-rich fluids. This is consistent with the high dihedral angle of carbonic fluids, and may be interpreted in terms of evolving fluid compositions within the shear zone.     

Microbial remains in some earliest Earth rocks: Comparison with a potential modern analogue

Carbonaceous matter (CM) from ca. 3.5 Ga hydrothermal black cherts of the Pilbara Craton of Western Australia and the Barberton Greenstone Belt of South Africa yielded transmission electron microscopy (TEM) images that are suggestive of microbial remains and possible remnants of microbial cell walls. These are compared to a potential modern analogue, the hyperthermophilic Methanocaldococcus jannaschii, derived from an active seafloor hydrothermal environment and cultured under similar conditions. A striking resemblance to the early Archaean forms was evident in wall structure and thermal degradation mode. Cell disintegration of the cultures occurred at 100 °C marking the limits of life. Complete disintegration, deformation and shrinkage occurred at 132 °C. A multidisciplinary approach to the characterisation of the CM was undertaken using organic petrology, TEM coupled with electron dispersive spectral analysis (EDS), high resolution TEM (HRTEM) to determine molecular ordering, and elemental and carbon isotope geochemistry. Reflectance measurements of the CM to determine thermal stress yielded a range of values corresponding to several populations, and pointing to different sources and processes. The δ¹³C values of Dresser Formation CM (−36.5 to −32.1‰) are negatively correlated with TOC (0.13–0.75%) and positively correlated with C/N ratio (134–569), which is interpreted to reflect the relative abundance of high R_o/oxidised/recycled CM and preferential loss of ¹²C and N during thermal maturation. TEM observations, inferred carbon isotopic heterogeneity and isotope fractionations of −27 to −32‰ are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM.     

Origin and Evolution of Silicic Magmatism at Yellowstone Based on Ion Microprobe Analysis of Isotopically Zoned Zircons

The origin of large-volume Yellowstone ignimbrites and smaller-volumeintra-caldera lavas requires shallow remelting of enormous volumesof variably ¹⁸O-depleted volcanic and sub-volcanic rocks alteredby hydrothermal activity. Zircons provide probes of these processesas they preserve older ages and inherited ¹⁸O values. This studypresents a high-resolution, oxygen isotope examination of volcanismat Yellowstone using ion microprobe analysis with an averageprecision of ± 0·2 and a 10 µm spot size.We report 357 analyses of cores and rims of zircons, and isotopeprofiles of 142 single zircons in 11 units that represent majorYellowstone ignimbrites, and post-caldera lavas. Many zirconsfrom these samples were previously dated in the same spots bysensitive high-resolution ion microprobe (SHRIMP), and all zirconswere analyzed for oxygen isotope ratios in bulk as a functionof grain size by laser fluorination. We additionally reportoxygen isotope analyses of quartz crystals in three units. Theresults of this work provide the following new observations.(1) Most zircons from post-caldera low-¹⁸O lavas are zoned,with higher ¹⁸O values and highly variable U–Pb ages inthe cores that suggest inheritance from pre-caldera rocks exposedon the surface. (2) Many of the higher-¹⁸O zircon cores in theselavas have U–Pb zircon crystallization ages that postdatecaldera formation, but pre-date the eruption age by 10–20kyr, and represent inheritance of unexposed post-caldera sub-volcanicunits that have ¹⁸O similar to the Lava Creek Tuff. (3) Youngand voluminous 0·25–0·1 Ma intra-calderalavas, which represent the latest volcanic activity at Yellowstone,contain zircons with both high-¹⁸O and low-¹⁸O cores surroundedby an intermediate-¹⁸O rim. This implies inheritance of a varietyof rocks from high-¹⁸O pre-caldera and low-¹⁸O post-calderaunits, followed by residence in a common intermediate-¹⁸O meltprior to eruption. (4) Major ignimbrites of Huckleberry Ridge,and to a lesser extent the Lava Creek and Mesa Falls Tuffs,contain zoned zircons with lower-¹⁸O zircon cores, suggestingthat melting and zircon inheritance from the low-¹⁸O hydrothermallyaltered carapace was an important process during formation ofthese large magma bodies prior to caldera collapse. (5) The¹⁸O zoning in the majority of zircon core–rim interfacesis step-like rather than smoothly inflected, suggesting thatprocesses of solution–reprecipitation were more importantthan intra-crystalline oxygen diffusion. Concave-downward zirconcrystal size distributions support dissolution of the smallercrystals and growth of rims on larger crystals. This study suggeststhat silicic magmatism at Yellowstone proceeded via rapid, shallow-levelremelting of earlier erupted and hydrothermally altered Yellowstonesource rocks and that pulses of basaltic magma provided theheat for melting. Each post-caldera Yellowstone lava representsan independent homogenized magma batch that was generated rapidlyby remelting of source rocks of various ages and ¹⁸O values.The commonly held model of a single, large-volume, super-solidus,mushy-state magma chamber that is periodically reactivated andproduces rhyolitic offspring is not supported by our data. Rather,the source rocks for the Yellowstone volcanism were cooled belowthe solidus, hydrothermally altered by heated meteoric watersthat caused low ¹⁸O values, and then remelted in distinct pocketsby intrusion of basic magmas. Each packet of new melt inheritedzircons that retained older age and ¹⁸O values. This interpretationmay have significance for interpreting seismic data for crustallow-velocity zones in which magma mush and solidified areasexperiencing hydrothermal circulation occur side by side. Newbasalt intrusions into this solidifying batholith are requiredto form the youngest volcanic rocks that erupted as independentrhyolitic magmas. We also suggest that the Lava Creek Tuff magmawas already an uneruptable mush by the time of the first post-calderaeruption after 0·1 Myr of the climactic caldera-formingeruption. KEY WORDS: Yellowstone; oxygen isotopes; geochronology; isotope zoning; zircon; U–Pb dating; caldera; rhyolite; ion microprobe     

Metamorphic fluid origins in the Osborne Fe oxide–Cu–Au deposit,Australia: evidence from noble gases and halogens

The Osborne iron oxide–copper–gold (IOCG) deposit is hosted by amphibolite facies metasedimentary rocks and associated with pegmatite sheets formed by anatexis during peak metamorphism. Eleven samples of ore-related hydrothermal quartz and two pegmatitic quartz–feldspar samples contain similarly complex fluid inclusion assemblages that include variably saline (<12–65 wt% salts) aqueous and liquid carbon dioxide varieties that are typical of IOCG mineralisation. The diverse fluid inclusion types present in each of these different samples have been investigated by neutron-activated noble gas analysis using a combination of semi-selective thermal and mechanical decrepitation techniques. Ore-related quartz contains aqueous and carbonic fluid inclusions that have similar ⁴⁰Ar/³⁶Ar values of between 300 and 2,200. The highest-salinity fluid inclusions (47–65 wt% salts) have calculated ³⁶Ar concentrations of approximately 1–5 ppb, which are more variable than air-saturated water (ASW = 1.3–2.7 ppb). These fluid inclusions have extremely variable Br/Cl values of between 3.8 × 10⁻³ and 0.3 × 10⁻³, and I/Cl values of between 27 × 10⁻⁶ and 2.4 × 10⁻⁶ (all ratios are molar). Fluid inclusions in the two pegmatite samples have similar ⁴⁰Ar/³⁶Ar values of ≤1,700 and an overlapping range of Br/Cl and I/Cl values. High-salinity fluid inclusions in the pegmatite samples have 2.5–21 ppb ³⁶Ar, that overlap the range determined for ore-related samples in only one case. The fluid inclusions in both sample groups have ⁸⁴Kr/³⁶Ar and ¹²⁹Xe/³⁶Ar ratios that are mainly in the range of air and air-saturated water and are similar to mid-crustal rocks and fluids from other settings. The uniformly low ⁴⁰Ar/³⁶Ar values (<2,200) and extremely variable Br/Cl and I/Cl values do not favour a singular or dominant fluid origin from basement- or mantle-derived magmatic fluids related to A-type magmatism. Instead, the data are compatible with the involvement of metamorphic fluids that have interacted with anatectic melts to variable extents. The ‘metamorphic’ fluids probably represent a mixture of (1) inherited sedimentary pore fluids and (2) locally derived metamorphic volatilisation products. The lowest Br/Cl and I/Cl values and the ultra-high salinities are most easily explained by the dissolution of evaporites. The data demonstrate that externally derived magmatic fluids are not a ubiquitous component of IOCG ore-forming systems, but are compatible with models in which IOCG mineralisation is localised at sites of mixing between fluids of different origin. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Oceanography in northwestern Europe during the last interglacial from intrashell δO ranges in Littorina littorea gastropods

Coastal sea-surface temperature (SST) and sea-surface salinity (SSS), including seasonality, in northwest (NW) Europe during the early phase of the Eemian interglacial ca. 125 ka ago were reconstructed from Littorina littorea (common periwinkle) gastropods. The results were based on intra-annual δ¹⁸O analyses in recent and fossil shells, mainly originating from the sea of Kattegat (Sweden) and the English Channel (United Kingdom), and confined to intertidal settings. The Eemian L. littorea shells indicated annual SSTs in the range 8–18°C for the English Channel and 8–26°C for Kattegat. All specimens from the Eemian sites experienced summer SSTs of ca. 1–3°C above recent conditions. The estimated winter SST in the English Channel during the Eemian was comparable to modern measurements of ca. 8°C. However, the Kattegat region displayed Eemian winter SST approximately 8°C warmer than today, and similar to conditions in the western English Channel. The recent-fossil isotope analogue approach indicated high SSS above 35 practical salinity units (psu) for a channel south of England in full contact with the North Atlantic Ocean during the last interglacial. In addition, the Kattegat shells indicated a SSS of ca. 29 psu, which points out a North Sea affinity for this region during the Eemian.