Hydrocarbons in surficial sediments from the Scotian Shelf

Surface sediments from 20 stations on the Scotian Shelf, collected on a transect from Halifax to Emerald Bank and around Sable Island, have been analyzed for hydrocarbon content and composition by gas chromatography and fluorescence spectrophotometry. Some samples were taken near abandoned exploratory drilling sites in the Sable Island area. Hydrocarbons appear to be mainly derived from biogenic terrestrial sources as evidenced by an inverse correlation of concentration with increasing distance from the mainland and a strong odd carbon preference in the n-alkanes. Contribution from petroleum sources, while minor, was most noticeable between Halifax and Emerald Bank. There is also evidence that the hydrocarbon composition at abandoned exploratory drilling sites has been slightly altered.     

Amino acid composition of organic matter associated with carbonate and non-carbonate sediments

Amino acids comprise from 15 to 36% by weight of humic substances from carbonate and non-carbonate sediments. Humic and fulvic acids extracted from carbonate sediments are characterized by an amino acid composition consisting primarily of the acidic amino acids, aspartic and glutamic acid. Humic substances from non-carbonate sediments have a distinctly different amino acid composition consisting primarily of glycine and alanine. Amino acid analyses of various molecular weight fractions of fulvic acids extracted from carbonates show that lower molecular weight fractions have appreciably higher relative abundances of the acidic amino acids compared to higher molecular weight fractions. Based on typical values for carboxyl group content in humic substances, acidic amino acids may be a significant contributor of these functional groups. Carbonate surfaces appear to selectively adsorb aspartic acid-enriched organic matter while non-carbonates do not have this property.     

Implications of abundant hygroscopic minerals in the Martian regolith

Converging lines of evidence suggest that a significant portion of the Martian surface fines may consist of salts and smectite clays. Salts can form stoichiometric hydrates as well as eutectic solutions with depressed freezing points; clays contain bound water of constitution and adsorb significant quantities of water from the vapor phase. The formation of ice may be suppressed by these minerals in some regions on Mars, and their presence in abundance would imply important consequences for atmospheric and geologic processes and the prospects for exobiology.     

Martian glaciation and the flow of solid CO2

The flow law determined experimentally for solid CO₂ establishes that a hypothesis of glacial flow of CO₂ at the Martian poles is not physically unrealistic. Compression experiments carried out under 1 atm pressure and constant strain rate demonstrate that the strength of CO₂ near its sublimation point is considerably less than the strength of water ice near its melting point. The data fit a power law “creep” equation of the form

$\text{?}\text{?}\text{= (4 × 10}{}^6\text{) σ}{}^{3.9}\text{exp}\text{(}\text{?12 200}\text{RT}\text{)}$

, where ? is compressive strain rate (sec^?1), σ is compressive stress (bars), R is the gas constant in calories per mole, and T is absolute temperature. The exponent of σ of 3.9 contrasts with a value near 3.1 for water ice, and indicates that the strain rate is somewhat more sensitive to stress for CO₂ than for water. Likewise, the low activation energy for creep, 12 200 cal mole^?1, illustrates that CO₂ is not highly sensitive to temperature and is thus likely to flow over a broad range of temperatures below its melting point. Strength values for CO₂ are of the order of one-tenth to one-third the strength of ice under equivalent conditions.A plausible glacial model for the Martian polar caps can be constructed and is helpful in explaining the unique character of the polar regions. CO₂-rich layers deposited near the pole would have flowed outward laterally to relieve high internal shear stresses. The topography of the polar caps, the uniform layering of the layered deposits, and the general extent of the polar “sediments” could all be explained using this model. Flow of CO₂ rather than water ice greatly reduces the problems with Martian glaciation. Nevertheless, problems do remain, in particular the large amounts of CO₂ necessary, the need to increase vapor pressure and temperature with depth in the polar deposits, and the lack of good observational evidence of flor features. Within the limits of the present knowledge of surface conditions of Mars, CO₂ glaciation appears to be a realistic alternate working hypothesis for the origin of the polar features.     

Surface properties of asteroids: A synthesis of polarimetry,radiometry, and spectrophotometry

The surface compositions of 110 asteroids are analyzed from statistically representative data sets of polarimetry as a function of phase angle, broad-band radiometry near 10 and 20 μm, and visible and near-infrared spectrophotometry. A comparison of albedos and diameters determined by polarimetry and radiometry shows that a modest upward revision of the radiometric albedo scale is needed and that a single law relating the slope of the polarization-phase curve to geometric albedo may not hold for very dark asteroids. We present reliable adopted albedos and diameters for 56 objects. Roughdi ameters for 52 additional objects are obtained from spectrophotometry using a correlation between albedo and color. Corrections for sampling bias permit investigation of asteroid compositions as a function of diameter, orbit, and other parameters.More than 90% of the minor planets fall into two broad compositional groups, defined by several optical parameters, designated by the symbols C and S. Comparisons with meteorite spectral albedo curves suggest that the two groups are compositionally similar to carbonaceous and stony-metallic meteorites, respectively. C-type asteroids predominate in the belt, especially in the outer half. An unusual distribution of compositions is found between 2.77 and 3.0 AU. Many S-type objects have diameters of 100–200 km; C-type objects are much more common at both larger and smaller sizes. Vesta is unique, being apparently the only differentiated asteroid remaining intact in the belt. The largest C-type objects are compositionally distinct from smaller ones and possibly are metamorphosed. We sketch some implications for meteoritics and for the early history of the solar system and point to the need for further systematic sampling of smaller and fainter objects by these three observational techniques.     

The spectral reflectivity of select areas on Europa

The July 12, 1973, occultation of Europa by Io was observed in 30 wavelength channels in the spectral region λλ3200-11, 000 Å with the 200-inch Hale telescope and a multichannel spectrometer. The data are presented in absolute units above the Earth's atmosphere. The data are analyzed to obtain the spectral reflectivity of seven localized areas on the disk of Europa centered on 324°W longitude. The equatorial material is confirmed to be darker than the eastward-skewed bright north polar cap and a hint is evident that the darker material as well may be somewhat redder than the cap material.     

Oil-generation kinetics for organic facies with Type-II and -IIS kerogen in the Menilite Shales of the Polish Carpathians

The Menilite Shales (Oligocene) of the Polish Carpathians are the source of low-sulfur oils in the thrust belt and some high-sulfur oils in the Carpathian Foredeep. These oil occurrences indicate that the high-sulfur oils in the Foredeep were generated and expelled before major thrusting and the low-sulfur oils in the thrust belt were generated and expelled during or after major thrusting. Two distinct organic facies have been observed in the Menilite Shales. One organic facies has a high clastic sediment input and contains Type-II kerogen. The other organic facies has a lower clastic sediment input and contains Type-IIS kerogen. Representative samples of both organic facies were used to determine kinetic parameters for immiscible oil generation by isothermal hydrous pyrolysis and S₂ generation by non-isothermal open-system pyrolysis. The derived kinetic parameters showed that timing of S₂ generation was not as different between the Type-IIS and -II kerogen based on open-system pyrolysis as compared with immiscible oil generation based on hydrous pyrolysis. Applying these kinetic parameters to a burial history in the Skole unit showed that some expelled oil would have been generated from the organic facies with Type-IIS kerogen before major thrusting with the hydrous-pyrolysis kinetic parameters but not with the open-system pyrolysis kinetic parameters. The inability of open-system pyrolysis to determine earlier petroleum generation from Type-IIS kerogen is attributed to the large polar-rich bitumen component in S₂ generation, rapid loss of sulfur free-radical initiators in the open system, and diminished radical selectivity and rate constant differences at higher temperatures. Hydrous-pyrolysis kinetic parameters are determined in the presence of water at lower temperatures in a closed system, which allows differentiation of bitumen and oil generation, interaction of free-radical initiators, greater radical selectivity, and more distinguishable rate constants as would occur during natural maturation. Kinetic parameters derived from hydrous pyrolysis show good correlations with one another (compensation effect) and kerogen organic-sulfur contents. These correlations allow for indirect determination of hydrous-pyrolysis kinetic parameters on the basis of the organic-sulfur mole fraction of an immature Type-II or -IIS kerogen.     

An experimental study of anorthosite dissolution in lunar picritic magmas: Implications for crustal assimilation processes

Experiments characterizing the kinetics of anorthosite dissolution in lunar picritic magmas (very low-Ti, low-Ti, and high-Ti picritic glasses) were conducted at 0.6 GPa and 1250-1400 °C using the dissolution couple method. Reaction between the anorthosite and lunar picritic magmas at 1250-1300 °C produced a spinel + melt layer. Reaction between the anorthosite and an olivine-saturated low-Ti magma at 1250-1300 °C produced a crystal-free region between the spinel + melt layer and the olivine-saturated magma. The anorthosite dissolution experiments conducted at 1400 °C simply dissolved anorthosite and did not result in a crystal-bearing region. The rate of anorthosite dissolution strongly depends on temperature and composition of the reacting melt. Concentration profiles that develop during anorthosite dissolution are nonlinear and extend from the picritic glass compositions to anorthite. These profiles feature a large and continuous variation in melt density and viscosity from the anorthosite-melt interface to the initial picritic magmas. In both the low-Ti and high-Ti magmas the diffusive fluxes of TiO₂, Al₂O₃, and SiO₂ are strongly coupled to the concentration gradients of CaO and FeO. Anorthosite dissolution may play an important role in producing the chemical variability of the lunar picritic magmas, the origin of spinel in the lunar basalts and picritic glasses, and the petrogenesis of the high-Al basalts.     

GGR Critical Review of Analytical Developments in 2004–2005

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.