Martin B. Goldhaber

Thermodynamics and kinetics of reactions involving vanadium in natural systems: Accumulation of vanadium in sedimentary rocks

A critical review of thermodynamic data for aqueous and solid V species is presented to evaluate dissolution, transport, and precipitation of V under natural conditions. Emphasis is given to results of experimental studies of V chemistry, especially those for which the experimental conditions are near those found in nature. Where possible, data are obtained for or corrected to the reference conditions of 298.15K, 1 atm (1.01325 bar) and zero ionic strength. Vanadium [IV] (VIV) and vanadium[V] (VV) are the most soluble forms of V in nature, and their complexes with fluoride, sulfate, and oxalate may act to increase V solubility under oxidizing conditions. Because redox behavior is of fundamental importance to understanding natural V chemistry, the kinetics of reduction of VIV to VIII H2S were studied. Although H2S is predicted from thermodynamic data to be capable of reducing VIV to VIII, this reaction has not been demonstrated experimentally. Experiments were carried out under conditions of temperature (45°C), pH (3.6–6.8), ionic strength (0.05–0.1 m), and V concentrations (9.8–240 μmolar) likely to be found in nature. Because the reaction is very slow, H2S concentrations in excess of natural conditions were used (8.1 × 10−4 to 0.41 atm). The results show that VIV is reduced to VIII under a variety of conditions. The rate increases with increasing pH, but is not appreciably affected by ionic strength (as represented by the concentration of KCl, which was used as the supporting electrolyte in all cases). Prior to initiation of the reaction, there is an induction period, the length of which increases with increasing KCl concentration or decreasing pH. Attempts to model the reaction mechanism by numerical methods have failed to produce a satisfying fit of the results, indicating partial reaction orders, a complex mechanism, or involvement of a variety of intermediate species. The results of the thermodynamic and kinetic studies were applied to understanding the genesis of V deposits such as those commonly found on the Colorado Plateau. Vanadium in these sandstone-hosted deposits is present mostly in the reduced oxidation state, VIII. Because of the insolubility of VIII oxyhydroxides, it is likely that a more oxidized form of V (either [IV] or [V]) was transported to the site of mineralization, and that the V was reduced in situ and subsequently precipitated. A probable reductant is hydrogen sulfide; the presence of pyrite cogenetic with the V minerals documents the presence of H2S during mineralization. The experiments described here show that H2S could have reduced VIV to V III, and thus led to the formation of these deposits.

Biogeochemical cycling in an organic-rich coastal marine basin. 7. Sulfur mass balance, oxygen uptake and sulfide retention

Sulfur and oxygen fluxes were quantified in the seasonally varying anoxic marine sedimentary system of Cape Lookout Bight, N.C., U.S.A. Over the three year study period, 1981–1983, the mean annual sulfate reduction rate was determined to be 18.2 ± 1.6 moles · m−2 · y−1. This value, added to the estimate of the detrital sulfur input of 1.2 ± 4.4 gave a total sulfur input of 19.4 ± 4.7 moles · m−2 · y−1. The sulfide flux to the sediment-water interface, measured in anaerobic benthic chambers was 4.6 ± 0.5 moles · m−2 · y−1, and represented 37% of the annual oxygen uptake rate of 25.2 ± 2.8 moles · m−2 · y−1. The sulfide burial rate, determined to be 15.5 ± 3.1 moles · m−2 · y−1, was within 5% of the value predicted by summing the fluxes at the sediment-water interface. The CS weight ratio of sediment below the depth of diagenetic reaction was determined to be 2.75. The sulfide retention rate in these rapidly accumulating sediments (10 cm/yr) was 77 ± 19%. Comparison of this result with previous studies shows that rapid sediment accumulation and the lack of bioturbation control this unusually high degree of sulfide retention.

An analytical scheme for determining forms of sulphur in oil shales and associated rocks

An analytical scheme for determining various forms of sulphur in oil shales and associated rocks is presented. Acid-soluble sulphate, sulphur contained in monosulphide and in disulphide minerals, and organically-bound sulphur are all quantitatively recovered as separate fractions. Finely-ground oil-shale samples are treated in an inert atmosphere with 6M hydrochloric acid to dissolve the acid-soluble sulphate minerals and form H(2)S from the decomposition of monosulphide minerals. The acid-soluble sulphate is precipitated as barium sulphate and the H(2)S is collected and weighed as silver sulphide. Disulphide minerals in the solid residue from the acid treatment are reduced by an acidified Cr(II) solution in an inert atmosphere, releasing the sulphide as H(2)S. The H(2)S is collected as silver sulphide. An Eschka fusion oxidizes and solubilizes all sulphur remaining within the Cr(II)-treated residue. This sulphate represents organically-bound sulphur and is collected as barium sulphate. The analytical procedures have been verified by using (57)Fe Mössbauer spectroscopy. Good agreement between the chemical and Mössbauer data substantiated the sequential removal of the forms of sulphur and also demonstrated the ability of Mössbauer spectroscopy to determine the absolute quantities of iron present in specific minerals.

Biogeochemical cycling in an organic-rich coastal marine basin. 8. A sulfur isotopic budget balanced by differential diffusion across the sediment-water interface

Abstract The sulfur isotopic composition of the sulfur fluxes occurring in the anoxic marine sediments of Cape Lookout Bight, N.C., U.S.A., was determined, and the result of isotopic mass balance was obtained via the differential diffusion model. Seasonal pore water sulfate δ 34 S measurements yielded a calculated sulfate input of 0.6%.. Sulfate transported into the sediments via diffusion appeared to be enriched in the lighter isotope because its concentration gradient was steeper, due to the increase in the measured isotopic composition of sulfate with depth. Similarly, the back diffusion of dissolved sulfide towards the sediment-water interface appeared enriched in the heavier isotope. The isotopic composition of this flux was calculated from measurements of the δ 34 S of dissolved sulfide and was determined to be 15.9%.. The isotopic composition of buried sulfide was determined to be −5.2%. and the detrital sulfur input was estimated to be −6.2%.. An isotope mass balance equation based upon the fluxes at the sediment-water interface successfully predicted the isotopic composition of the buried sulfur flux within 0.5%., thus confirming that isotopes diffuse in response to their individual concentration gradients.

Origin of minerals in joint and cleat systems of the Pottsville Formation, Black Warrior basin, Alabama: Implications for coalbed methane generation and production

Coalbed methane is produced from naturally fractured strata in the lower Pennsylvanian Pottsville Formation in the eastern part of the Black Warrior basin, Alabama. Major fracture systems include orthogonal fractures, which consist of systematic joints in siliciclastic strata and face cleats in coal that strike northeast throughout the basin. Calcite and minor amounts of pyrite commonly fill joints in sandstone and shale and, less commonly, cleats in coal. Joint-fill calcite postdates most pyrite and is a weakly ferroan, coarse-crystalline variety that formed during a period of uplift and erosion late in the burial history. Pyrite forms fine to coarse euhedral crystals that line joint walls or are complexly intergrown with calcite.Stable-isotope data reveal large variations in the carbon isotope composition of joint- and cleat-fill calcite (10.3 to +24.3 Peedee belemnite [PDB]) but only a relatively narrow range in the oxygen-isotope composition of this calcite (16.2 to 4.1 PDB). Negative carbon values can be attributed to 13C-depleted CO2 derived from the oxidation of organic matter, and moderately to highly positive carbon values can be attributed to bacterial methanogenesis. Assuming crystallization temperatures of 2050C, most joint- and cleat-fill calcite precipitated from fluids with 18O ratios ranging from about 11 to +2 standard mean ocean water (SMOW). Uplift and unroofing since the Mesozoic led to meteoric recharge of Pottsville strata and development of freshwater plumes that were fed by meteoric recharge along the structurally upturned, southeastern margin of the basin. Influxes of fresh water into the basin via faults and coalbeds facilitated late-stage bacterial methanogenesis, which accounts for the high gas content in coal and the carbonate cementation of joints and cleats.Diagenetic and epigenetic minerals can affect the transmissivity and storage capacity of joints and cleats, and they appear to contribute significantly to interwell heterogeneity in the Pottsville Formation. In highly productive coalbed methane fields, joint- and cleat-fill calcite have strongly positive 13C values, whereas calcite fill has lower 13C values in fields that are shut in or abandoned. Petrographic analysis and stable-isotope geochemistry of joint- and cleat-fill cements provide insight into coalbed methane reservoir quality and the nature and extent of reservoir compartmentalization, which are important factors governing methane production.

Iron sulfide minerals at Cement oil field, Oklahoma: Implications for magnetic detection of oil fields

Aeromagnetic anomalies at Cement oil field (Anadarko basin, Oklahoma) have been attributed to authigenic magnetite. The following characteristics of the magnetite, however, indicate that it is contamination introduced by drilling: (1) occurrence as sharp angular blades and as spheres, commonly with metallographic textures typical of industrial alloys and with associated steel and wustite (FeO); (2) presence only in well cuttings and absence from core and quarry samples; and (3) lack of association with detrital framework grains or with authigenic carbonate and sulfide minerals. Ferrimagnetic pyrrhotite occurs in well cuttings, cores, and quarry samples at Cement and is a possible natural source of the magnetic anomalies. Pyrrhotite, which is intergrown with more abundant FeS 2 minerals, formed as a result of hydrocarbon seepage. Pyrrhotite is confined to beds above oil and gas reservoirs. These beds, which lack detrital organic matter, contain higher mineral sulfide and lower mineral sulfate sulfur (1.7 and 0.1 wt %, respectively) than do correlative beds off the field (0.2 and 1.1 wt %, respectively). In the field, isotopic values of sulfide S show a systematic decrease upward through the Permian section from positive values (maximum, +12 per mil at ∼610-760 m depth) to negative values (-1 to -11 per mil between 32 and 230 m; -26 to -30 per mil at the surface). Geochemical results, together with time-temperature data derived from burial curves, limit the major sources of the sulfide in the Fe-S minerals to two possibilities. Isotopically heavy sulfide was generated either inorganically at temperatures >∼90 °C in beds beneath Permian beds, or by bacterial sulfate reduction at temperatures

Regional fluid flow as a factor in the thermal history of the Illinois basin: Constraints from fluid inclusions and the maturity of Pennsylvanian coals

Vitrinite reflectance measurements on Pennsylvanian coals in the Illinois basin indicate significantly higher thermal maturity than can be explained by present-day burial depths. An interval of additional sedimentary section, now removed by erosion, has been suggested to account for the discrepancy. Although burial could indeed account for the observed maturity levels of organic matter, fluid-inclusion temperatures provide a stringent additional constraint. In this article, we combine measurements of coal maturity with fluid-inclusion temperatures from three sites to constrain the basins thermal and burial history: the Fluorspar district at the Illinois basins southern margin, the Upper Mississippi Valley zinc district at the basins northern margin, and a north-central location. Two-dimensional numerical modeling of a north-south cross section through the basin tests scenarios both with and without regional fluid flow. Vitrinite reflectance values can be matched assuming burial by 1.8-2.8 km of southward-thickening additional, post-Pennsylvanian sedimentary section. In the central and northern Illinois basin, however, these burial depths and temperatures are not sufficient to account for the fluid-inclusion data. To account for both parameters with burial alone does not appear feasible. In contrast, our best hypothesis assumes a wedge of post-Pennsylvanian sediment-thickening southward to about 1.2 km and a brief period of magmatism in the Fluorspar district. Significant advective heat redistribution by northward regional fluid flow accounts for fluid-inclusion temperatures and coal maturities throughout the basin. The modeling results demonstrate the potential contribution of advective heat transport to the thermal history of the Illinois basin. (Begin page 258)

Sedimentary sulfur geochemistry of the Paleogene Green River Formation, western USA: Implications for interpreting depositional and diagenetic processes in saline alkaline lakes

Abstract The sulfur geochemistry of the lacustrine Paleogene Green River Formation (Colorado, Utah, and Wyoming, USA) is unlike that of most marine and other lacustrine rocks. Distinctive chemical, isotopic, and mineralogical characteristics of the formation are pyrrhotite and marcasite, high contents of iron mineral sulfides strikingly enriched in 34 S, cyclical trends in sulfur abundance and δ 34 S values, and long-term evolutionary trends in δ 34 S values. Analyses that identified and quantified these characteristics include carbonate-free abundance of organic carbon (0.13–47 wt%), total iron (0.31–13 wt%), reactive iron (>70% of total iron), total sulfur (0.02–16 wt%), acid-volatile monosulfide (S Av ), disulfide (S Di > 70% of total sulfur), sulfate (S SO 4 ) and organosulfur (S Org ); isotopic composition of separated sulfur phases (δ 34 S Di,Av up to +49‰); and mineralogy, morphology and paragenesis of sulfide minerals. Mineralogy, morphology, δ 34 S Di,Av , and δ 34 S Org have a distinctive relation, reflecting variable and unique depositional and early diagenetic conditions in the Green River lakes. When the lakes were brackish, dissimilatory sulfate-reducing bacteria in the sediment produced H 2 S, which initially reacted with labile iron to form pyrite framboids and more gradually with organic matter to form organosulfur compounds. During a long-lived stage of saline lake water, the amount of sulfate supplied by inflow decreased and alkalinity and pH of lake waters increased substantially. Extensive bacterial sulfate reduction in the water column kept lake waters undersaturated with sulfate minerals. A very high H 2 S:SO 4 ratio developed in stagnant bottom water aided by the high pH that kinetically inhibited iron sulfidization. Progressive removal of H 2 S by coeval formation of iron sulfides and organosulfur compounds caused the isotopic composition of the entire dissolved sulfur reservoir to evolve to δ 34 S values much greater than that of inflow sulfate, which is estimated to have been +20‰ A six-million-year interval within Lake Uinta cores records this evolution as well as smaller systematic changes in δ 34 S, interpreted to reflect ~ 100,000-year lake-level cycles. When porewater was exceptionally reducing, unstable FeS phases eventually recrystallized to pyrrhotite during diagenesis. A much later reaction related to weathering altered pyrrhotite to marcasite.

Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate

Abstract A simple procedure for preparing barite samples for chemical and isotopic analysis is described. Sulfate ion, in barite, in the presence of high concentrations of aqueous sodium carbonate, is replaced by carbonate. This replacement forms insoluble carbonates with the cations commonly in barite: Ba, Sr, Ca and Pb. Sulfate is released into the solution by the carbonate replacement and is separated by filtration. The aqueous sulfate can then be reprecipitated for analysis of the sulfur and oxygen isotopes. The cations in the carbonate phase can be dissolved by acidifying the solid residue. Sr can be separated from the solution for Sr isotope analysis by ion-exchange chromatography. The sodium carbonate used contains amounts of Sr which will affect almost all barite 87 Sr 86 Sr ratios by less than 0.00001 at 1.95θ of the mean. The procedure is preferred over other techniques used for preparing barite samples for the determination of 87 Sr 86 Sr ratios because it is simple, rapid and enables simultaneous determination of many compositional parameters on the same material.

Depositional Setting and Diagenetic Evolution of Some Tertiary Unconventional Reservoir Rocks, Uinta Basin, Utah

The Douglas Creek Member of the Tertiary Green River Formation underlies much of the Uinta basin, Utah, and contains large volumes of oil and gas trapped in a complex of fractured low-permeability sandstone reservoirs. In the southeastern part of the basin at Pariette Bench, the Eocene Douglas Creek Member is a thick sequence of fine-grained alluvial sandstone complexly intercalated with lacustrine claystone and carbonate rock. Sediments were deposited in a subsiding intermontane basin along the shallow fluctuating margin of ancient Lake Uinta. Although the Uinta basin has undergone postdepositional uplift and erosion, the deepest cored rocks at Pariette Bench have never been buried more than 9,800 ft (3,000 m). The sandstones, dominantly lithic arkoses and feldspathic litharenites, were derived from source terranes south of the Uinta basin. Secondary silica and several generations of authigenic calcite [Ca1.8-1.9(Mg0.02-0.06Fe0.02-0.06)(CO3)2], dolomite [Ca1.3-1.4(Mg0.6-0.7Fe0.02-0.04)(CO3)2], and ankerite [Ca1.2-1.3(Mg0.2-0.3Fe0.4-0.6)(CO3)2] form a replacive cement in the sandstones. Commonly, syntaxial overgrowths of late iron-bearing carbonate occur on detrital grains and preexisting relicts of iron-free carbonate cement. In sandstone where carbonate has been partly dissolved, abundant authigenic illite, partly ordered mixed- ayer illite-smectite, and small amounts of chlorite partly to completely fill secondary pores. Isotopic composition of carbonate cement and grain-supported rock range from -0.39 to -6.18 ^pmil for ^dgr13C and -7.80 to -13.98 ^pmil for ^dgr18O, indicating that authigenic carbonate formed at low temperatures in the presence of meteoric waters by a process of solution-precipitation. Enrichment of carbon and oxygen in early diagenetic calcite and fossiliferous rock relative to late diagenetic ankerite indicates a trend toward lighter isotopic carbonate compositions with increasing diagenesis. Kerogenous rocks at Pariette Bench are thermochemically immature and therefore are not the source of oil produced in the field. Hydrocarbons are compositionally similar to some of the oils produced from the Green River Formation in the Bluebell-Altamont field and are interpreted to have migrated from mature Green River source rocks through a network of open fractures. The occurrence of small amounts of hydrocarbon in secondary pores indicates that its emplacement postdated carbonate dissolution.