Stenols and stanols in the oxic and anoxic waters of the Black Sea

Water samples collected from a slope station and two deep stations in the western basin of the Black Sea were analyzed for stenols and stanols by glass capillary gas chromatography. These results were used in conjuction with hydrographic, particulate organic carbon, and chlorophyll a data to better understand sterol sources and their transport and transformation mechanisms in anoxic basins.The total free sterol concentrations found in the surface waters were 450–500 ng/l dropping rapidly to values well below 100 ng/l at depths below the $\text{O}{}_2\text{H}{}_2\text{S}$ interface. In the upper 200 m of the water column a strong association of sterols with particulate matter is suggested. Structural elucidation by a gas chromatograph-mass spectrometer-computer system revealed the presence of at least sixteen different stenols and stanols in the surface waters of the Black Sea. Cholesterol, 24-methylenecholesterol and 24-methylcholesta-5,22-dien-3β-ol were the major sterols in the surface waters. Cholesterol and 24-ethylcholesterol both exhibited a subsurface maximum at the $\text{O}{}_2\text{H}{}_2\text{S}$ interface. In the anoxic deep waters (200–2000 m) only cholesterol and 24-ethylcholesterol were found. Two stenols were found that have not been reported in seawater: a C₂₆ stenol with a saturated C₇H₁₅ side chain (presumably 24-norcholesterol) and 24-ketocholesterol. At least six 5α-stanols could be identified in the surface samples, each of them comprising about 10–20% of the concentration of the corresponding Δ5-stenol. From these comparatively high surface values the stanol concentrations drop rapidly to values near zero at the $\text{O}{}_2\text{H}{}_2\text{S}$ interface. Except for very low concentrations of 5α-cholestanol (< 4ng/l) no other stanols could be detected in the anoxic zone.From this data it appears that no detectable stenol → stanol conversion is occurring at the $\text{O}{}_2\text{H}{}_2\text{S}$ interface or in the deep anoxic waters of the Black Sea.     

Chemical evidence of differential particle dispersal in the southern washington coastal environment

Aliphatic hydrocarbons, cupric oxide oxidation products of lignin and polycyclic aromatic hydrocarbons (PAH) were analyzed by capillary gas chromatography in sediments from the southern Washington continental shelf and slope. The concentration of diploptene relative to plantwax $\text{n-}\text{alkanes}$ increased systematically in surface sediments with distance offshore along east-west transects of the study area and remained constant in surface sediments along the midshelf silt deposit. Analogous trends were also observed for the concentration of cinnamyl phenols relative to vanillyl phenols and total methylphenanthrenes relative to phenanthrene. These changes in sedimentary composition are evidence that diploptene from some terrestrial source, lignin characteristic of non-woody vascular plant tissue and a fossil organic material contained within weathered rock debris disperse across the Washington continental shelf and slope in geographic patterns distinct from that for other river-derived, chemically related materials. The compositional variations are explained by the particulate associations of the land-derived chemicals and differential hydraulic dispersion of their respective carrier particles after discharge at the mouth of the Columbia River.     

Sorption of noble gases by solids,with reference to meteorites. I. Magnetite and carbon

To simulate trapping of meteoritic noble gases by solids, 18 samples of Fe₃O₄ were synthesized in a noble gas atmosphere at 350–720 K by the reactions: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ (Ne, Ar, Kr, Xe) 3Fe + 4CO → Fe₃O₃ + 4C + carbides (Xe only) Phases were separated by selective solvents (HgCl₂, HCl). Noble gas contents were analyzed by mass spectrometry, or, in runs where 36 d Xe¹²⁷ tracer was used, by γ-counting. Surface areas, as measured by the BET method, ranged from 1 to 400 m²/g. Isotopic fractionations were below the detection limit of 0.5%/m.u.Sorption of Xe on Fe₃O₄ and C obeys Henry's Law between $\text{1 × 10}{}^{\mathrm{?8}}$ and $\text{4 × 10}{}^{\mathrm{?5}}$ atm, but shows only a slight temperature dependence between 650 and 720 K ($\text{ΔH}{}_{\mathrm{sol}}\text{= ?4 ± 2}\text{kcal/mole}$). The mean distribution coefficient K_Xe is $\text{0.28 ± 0.09}$ cc STP/g atm for Fe₃O₄ and only a factor of $\text{1.2 ± 0.4}$ greater for C; such similarity for two cogenetic phases was predicted by Lewis et al. (1977). Stepped heating and etching experiments show that 20–50% of the total Xe is physically adsorbed and about 20% is trapped in the solid. The rest is chemisorbed with $\text{ΔH}{}_{\mathrm{s}}\text{? ?13}\text{kcal/mole}$. The desorption or exchange half-time for the last two components is >10² yr at room temperature.Etching experiments showed a possible analogy to “Phase $\text{Q}$” in meteorites. A typical carbon + carbide sample, when etched with HNO₃, lost 47% of its Xe but only 0.9% of its mass, corresponding to a ~0.6 Å layer. Though this etchable, surficial gas component was more thermolabile than $\text{Q}$ (release $\text{T}$ below 1000°C, compared to 1200–1600°C), another experiment shows that the proportion of chemisorbed Xe increases upon moderate heating (1 hr at 450°C). Apparently adsorbed gases can become “fixed” to the crystal, by processes not involving volume diffusion (recrystallization, chemical reaction, migration to traps, etc.). Such mechanisms may have acted in the solar nebula, to strengthen the binding of adsorbed gases.Adsorbed atmospheric noble gases are present in all samples, and dominate whenever the noble gas partial pressure in the atmosphere is greater than that in the synthesis. Many of the results of Lancet and Anders (1973) seem to have been dominated by such an atmospheric component; others are suspect for other reasons, whereas still others seem reliable. When the doubtful samples of Lancet and Anders are eliminated or corrected, the fractionation pattern—as in our samples—no longer peaks at Ar, but rises monotonically from Ne to Xe. No clear evidence remains for the strong temperature dependence claimed by these authors.     

Interstellar organic matter in meteorites

Hydrogen which is highly enriched in deuterium is present in organic matter in a variety of meteorites including non-carbonaceous chondrites. The concentrations of this hydrogen are quite large. For example Renazzo contains 140 μmoles/g of the 10,000‰ δD hydrogen. The $\text{D}\text{H}$ ratios of hydrogen in the organic matter vary from 8 × 10^?5 to 170 × 10^?5 (δD ranges from ? 500‰ to 10,000‰) as compared to 16 × 10^?5 for terrestrial hydrogen and 2 × 10^?5 for cosmic hydrogen. The majority of the unequilibrated primitive meteorites contain hydrogen whose $\text{D}\text{H}$ ratios are greater than 30 × 10^?5. If the $\text{D}\text{H}$ ratios in these compounds were due to enrichment relative to cosmic hydrogen by isotope exchange reactions, it would require that these reactions take place below 150 K. In addition the organic compounds having $\text{D}\text{H}$ ratios above 50 × 10^?5 would require temperatures of formation of < 120 K. These types of deuterium enrichments must take place by ion-molecule reactions in interstellar clouds where both ionization and low temperatures exist. Astronomically observed $\text{D}\text{H}$ ratios in organic compounds in interstellar clouds are typically 180 × 10^?5 and range between about 40 × 10^?5 and 5000 × 10^?5. The $\text{D}\text{H}$ values we have determined are the lower limits for the organic compounds derived from interstellar molecules because all processes subsequent to their formation, including terrestrial contamination, decrease their $\text{D}\text{H}$ ratios.In contrast, the $\text{D}\text{H}$ ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites we have analyzed with an average value of 14 × 10^?5; very similar to the terrestrial value. These phyllosilicates values suggest equilibration of H₂O with H₂ in the solar nebula at temperatures of about 200 K and higher.The ${}^{13}\text{C}{}^{12}\text{C}$ ratios of organic matter, irrespective its $\text{D}\text{H}$ ratio, lie well within those observed for the earth. If organic matter originated in the interstellar medium, our data would indicate that the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of interstellar carbon five billion years ago was similar to the present terrestrial value.Our findings suggest that other interstellar material, representing various inputs from various stars, in addition to the organic matter is preserved and is present in the meteorites which contain the high $\text{D}\text{H}$ ratios. We feel that some elements existing in trace quantities which possess isotopic anomalies in the meteorites may very well be such materials.     

Organic matter from a sediment trap experiment in the equatorial north Atlantic: wax esters,steryl esters,triacylglycerols and alkyldiacylglycerols

The vertical flux and composition of wax esters, steryl esters, triacylglycerols, and alkyldiacylglycerols in particulate matter was determined in the equatorial Atlantic Ocean by deploying sediment traps at 389, 988, 3,755 and 5,068 m. Detailed compositional analyses of these lipids were carried out by high temperature glass capillary gas chromatography and gas chromatography/mass spectrometry.The distributions of these lipids are discussed in terms of potential biological sources. Zooplankton fecal matter and intact zooplankters may represent the most important input of these compounds to the shallower two traps, while the material in the deeper two traps appears to have been biogeochemically altered. The finding of these biochemically important compounds, often unsaturated, indicates that particle transit through the water column must be relatively fast.Wax esters were most abundant in the 389 m sediment trap and decreased with increasing trap depth. Compounds ranging from C₂₈–C₄₄ were present at all depths. The major homologs were C₃₂, C₃₄ and C₃₆, most often monounsaturated. The dominant alcohol/acid combinations in the 389 m trap were $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{14:0}}$ and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{16:0}}$, but in the 988 m sample, $\text{C}{}_{\mathrm{16:0}}\text{C}{}_{\mathrm{18:1}}$ was the major wax ester. A flux maximum was observed for steryl esters at 988 m. Cholesteryl esters of C_14:0, C_16:1 and C_16:0, and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{18:0}}$ fatty acids were the dominant steryl esters. For triacylglycerols, fluxes in the 389 and 988 m traps were similar, while the deeper pair of traps contained much less triacylglycerol. C₄₆, C₄₈, C₅₀ and C₅₂ compounds were the major triacylglycerols. Constituent fatty acids in the 389 m and 988 m samples were mainly C_14:0, C_16:1, C_16:0, C_18:1 and C_18:0. In the 988 m material, C_20:5 and C_22:6 were also dominant. A homologous series of alkyldiacylglycerols was abundant in the 389 m trap material. The alkyldiacylglycerols consisted of C₄₆–C₅₆ compounds composed of C_16:0 alkyl moieties and C_14:0, C_16:0, C_18:1, and C_18:0 fatty acids.     

Kinetics of silica sorption and clay dissolution reactions at 1 and 670 atm

Rates of reactions between clay minerals and silica-spiked seawater and the effect of pressure on the direction, extent and rate of such reactions have been studied. Kinetic behavior of short-term, clay-silica reaction indicates that diffusion is the rate controlling process in both clay dissolution and clay reconstitution reactions. Rate constants of these reactions are of the order of 10^?13 moles/ sec^{$\text{1}\text{2}$}cm². No significant pressure effect on the rate of clay dissolution was observed. Estimates of diffusion coefficient of silicic acid for clay dissolution and silica sorption reactions indicate that the true value lies within the range, 10^?13–10^?17cm²/sec, thus reflecting the semicrystalline or amorphous nature of the reaction product through which diffusion is occurring.     

The role of carbon and oxygen in cosmic gases: some applications to the chemistry and mineralogy of enstatite chondrites

A new condensation sequence appears if the $\text{C}\text{O}$ ratio in a gas of otherwise solar composition is increased by less than a factor of two. As the ratio increases from the solar value of 0.6 to ? 1 the gas becomes extremely reduced, the condensation temperatures of silicates and oxides are depressed markedly ～ 400 K and a new suite of refractory minerals appears: AIN, CaS, MgS, SiC, TiN, graphite, Si₂N₂O and probably metastable (Fe,Ni)³C. Many of these minerals are unique to enstatite chondrites and may be analogues of the refractory silicates and oxides found in more oxidized meteorites such as Allende.The change in chemistry is related to the stability of CO, the most stable C or O compound at high T. Since the elements occur in a 1:1 ratio in CO, only the element which is in excess is free to form other compounds. But as T decreases CO reacts with H₂ to form graphite, CH₄ or other hydrocarbons thereby freeing O to form H₂O. If equilibrium is maintained oxides and silicates form at about 1000 K ($\text{C}\text{O}\text{> 1}$, P_τ = 10^?4atm) as products of reactions among the carbides, nitrides, sulfides and the gas. The possibility that equilibrium was not maintained among the C-bearing species was also investigated. If either graphite or CH₄ does not form as predicted the stability fields of the reduced minerals expands to lower temperatures. If neither graphite nor CH₄ form as predicted, CO remains stable and the nebular gas is highly reduced at all temperatures.Enstatite chondrites appear to have originated in a region of the nebula where the $\text{C}\text{O}$ ratio was somewhat higher than the solar value. Various fractionation mechanisms are considered. An interesting possibility is that graphite, which is quite refractory under a wide range of conditions, survived the collapse of the solar nebula.     

Ammonia-ammonium leaching of deep-sea manganese nodules

Ammonia-ammonium leaching of samples of nodules from several different locations was carried out after reduction of the nodules under $\text{CO}\text{CO}{}_2$ gas mixtures at 400, 600, and 800°C. In accordance with thermodynamic analysis, nickel, copper and cobalt oxides in the nodules are preferentially reduced with a $\text{60}\text{40}$ gas mixture of $\text{CO}\text{CO}{}_2$. After an initial reduction step with $\text{CO}\text{CO}{}_2$ at 600°C, leaching at room temperature and atmospheric pressure with aqueous ammonia-ammonium carbonate and ammonia-ammonium sulfate solutions yielded high extractions of copper and nickel (> 80%), and close to 50% for cobalt. The nature of the pores in nodules from different locations appears to affect the extraction process. A lower reduction temperature is required to obtain the same extraction of nickel, copper and cobalt in a sulfate system than is necessary in a carbonate system. However, a higher manganese content results in the sulfate leaching solutions as compared to the carbonate system, where essentially none of the manganese and iron are extracted.     

Non-equilibrium water/rock interactions—I. Model for interface-controlled reactions

The results of established crystal growth theory and silicate dissolution experiments are combined in developing a new model for mineral/water reactions controlled by surface processes. The overall reaction rate at steady-state is determined by coupling equations for the velocities of mass transport and interface detachment processes. Non-steady state processes can be successfully treated when interface reactions control the rate. For most sparingly soluble minerals, diffusion through the solution can be neglected as a rate-determining factor.Many surface processes are driven by the total interface under saturation, but only processes facilitating detachment contribute to dissolution. Other, non-detachment related, surface reactions result in lower dissolution rates. Slow rates of many mineral/solution reactions are attributed to the surface processes which consume the energy that would otherwise drive detachment.An analysis of the time dependence of interface reaction velocities indicates that linear rate laws apply when uniform detachment or layer-source generation mechanisms such as screw dislocations control the dissolution rate. At low interfacial undersaturations, first-order, logarithmic rate laws prevail. A parabolic time dependence occurs if surface detachment parameters vary as a function of (time)^{$\text{1}\text{2}$}.     

Alteration of basaltic glass: Mechanisms and significance for the oceanic crust-seawater budget

Alteration of basaltic glass to palagonite is characterized by a nearly isomolar exchange of SiO₂, Al₂O₃, MnO, MgO, CaO, Na₂O, P₂O₅, Zn, Cu, Ni, Cr, Hf, Sc, Co and REE for H₂O and K₂O, whilst TiO₂ and FeO are passively accumulated during removal of the remaining cations. The network forming cations Al and Si are removed from the glass in proportion to the gain in Ti and Fe, whilst the other cations do not show a significant relationship to the amount of Ti and Fe accumulation. Sr isotopic data show that during palagonite formation approximately 85% of the basaltic Sr is lost to the hydrous solutions and 40% of seawater Sr is added to the glass, yielding an average loss of the same order of magnitude as of the network forming cations. Losses and gains of oxides yield an average increase of +105% TiO₂.K, Rb, and Cs show high increases, but $\text{K}\text{Rb}$ and $\text{K}\text{Cs}$ ratios indicate two different alteration processes: (1) formation of palagonite involves a drastic decrease in these ratios, indicating structural similarities between palagonite and smectite; (2) surface alteration of glass is characterized by an increase in $\text{K}\text{Rb}$ and $\text{K}\text{Cs}$ ratios, probably best interpreted as sorption of alkalies in ratios approximating those of seawater.The total fluxes involved in alteration of glass in the upper portion of the oceanic crust are estimated from the modal abundance of palagonite in the oceanic crust and the abundance of the vein materials smectite and carbonate. Smectite and carbonates act as a sink for a significant portion of the elements liberated up during alteration of basaltic glass except for Na and Al, which are probably taken up by zeolites and/or albite, possibly hidden in the macroscopic estimate of carbonate. Formation of the observed quantity of secondary phases requires additional sources for Si, Fe. Ca and K. K is provided in excess from the inflowing seawater at reasonable water/rock ratios. The remaining excess Ca, Si and Fe required may be derived by alteration of interstitial glass and breakdown of anorthite rich plagioclase and titano-magnetite, and/or by supply of deeper seated metamorphic reactions.     

Etude des inclusions fluides du système N2-CO2 de dolomites et de quartz de Tunisie septentrionale. Données de la microcryoscopie et de l'analyse à la microsonde à effet Raman

Optical and analytical studies were performed on 400 N₂ + CO₂ gas bearing inclusions in dolomites and quartz from Triassic outcrops in northern Tunisia. Other fluids present include brines (NaCl and KCl bearing inclusions) and rare liquid hydrocarbons. At the time of trapping, such fluids were heterogeneous gas + brine mixtures. In hydrocarbon free inclusions the $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}$ mole ratio was determined using two different non-destructive and punctual techniques: Raman microprobe analysis, and optical estimation of the volume ratios of the different phases selected at low temperatures. In the observed range of compositions, the two methods agree reasonably well.The N₂ + CO₂ inclusions are divided into three classes of composition: (a) $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{> 0,57}$: Liquid nitrogen is always visible at very low temperature and homogenisation occurs in the range ?151°C to ? 147°C (nitrogen critical temperature) dry ice (solid CO₂) sublimates between ?75°C and ?60°C; (b) $\text{0,20 <}\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{? 0,57}$: liquid nitrogen is visible at very low temperature but dry ice melts on heating; liquid and gas CO₂ homogenise to liquid phase between ?51°C to ?22°C; (c) $\text{N}{}_2\text{(N}{}_2\text{+ CO}{}_2\text{)}\text{? 0,20}$: liquid nitrogen is not visible even at very low temperature (?195°C) and liquid and gas CO₂ homogenise to liquid phase between ?22°C and ?15°C. The observed phases changes are used to propose a preliminary phase diagram for the system CO₂-N₂ at low temperatures.Assuming additivity of partial pressures, isochores for the CO₂-N₂ inclusions have been computed. The intersection of these isochores with those for brine inclusions in the same samples may give the P and T of trapping of the fluids.     

Properties of gases and petroleum liquids derived from terrestrial kerogen at various maturation levels

This study deals mainly with shale-sandstone series in which the disseminated kerogen is mostly composed of land-derived debris. Organic matter was characterized by microscopic and chemical techniques. The kerogen maturity was assessed by microscopic studies, mainly by means of vitrinite reflectance measurements. The chemical properties of shale kerogens and of oil and gas shows, were examined in several sedimentary basins in different parts of the world.Oil and gas properties were tentatively interpreted in terms of maturity, using a comparison of oil properties with the kerogen features of shales interbedded in the impregnated sandstone reservoirs. The synthesis is documented in several case histories including those from New Zealand, Colombia, Australia, Indonesia.In low maturity stages (immature zone), dry gas with minor condensate is observed, whereas in higher maturity levels (oil window), wet gas with high paraffinic crudes is generally recorded. Pristane to n-C₁₇ ratios allow a distinction to be made between immature (often > 1.0) and mature (< 1.0) condensates, i.e. intensively cracked crude oils. I-C₄ to n-C₄ ratios enable an adequate discrimination to be made between gases produced with immature condensates ($\text{i-C}{}_4\text{n-C}{}_4\text{> 0.80}$) and those produced with high wax crudes or mature condensates ($\text{i-C}{}_4\text{n-C}{}_4\text{< 0.80}$). Shallow depth condensates and their related gases have been identified as immature fluids. Properties of some mature condensates are given as references.This study offers a maturity framework as a guide for oil and gas show prediction in shale-sandstone sequences containing land-derived kerogen.     

Aragonite from deep sea ultramafic rocks

Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content (< 0.03%) and higher Sr content (> 0.95%) relative to other marine aragonites. Their ${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg²⁺ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.     

Sorption of noble gases by solids,with reference to meteorites. III. Sulfides,spinels, and other substances; on the origin of planetary gases

To simulate trapping of noble gases by meteorites, we reacted 15 FeCr or FeCrNi alloy samples with CO, H₂O or H₂S at 350–720 K, in the presence of noble gases. The reaction products, including (Fe,Cr)₂O₃, FeCr₂S₄, FeS, C, and Fe₃C, were analyzed by mass spectrometry, usually after chemical separation by selective solvents. Three carbon samples were prepared by catalytic decomposition of CO or by dehydration of carbohydrates with H₂SO₄.The spinel and carbon samples were similar to those of earlier studies (Yang et al., 1982 and Yang and Anders, 1982), with only minor effects attributable to the presence of Ni. All samples sorted substantial amounts of noble gases, with distribution coefficients of 10^?1–10^?2 cm³ STP/g atm for Xe. On the basis of release temperature three gas components were distinguished: a generally dominant physisorbed component (20–80% of total), and two more strongly bound, chemisorbed and trapped components. Judging from the elemental pattern, the adsorbed components were acquired at the highest noble gas partial pressure encountered by the sample—atmosphere or synthesis vessel.Sulfides, particularly daubréelite, showed three distinctive trends relative to chromite or magnetite: the high-T component was larger, 30–70% of the total; $\text{Ne}\text{Xe}$ ratios were higher, by up to 10², possibly due to preferential diffusion of Ne during synthesis. In one synthesis, at relatively high P, the gases were sorbed with only minimal elemental fractionation, presumably by occlusion.Most of the features of primordial noble gases can be explained in terms of the data and concepts presented in the three papers of this series. The elemental fractionation pattern of Ar, Kr, Xe in meteorites, terrestrial rocks, and planets resembles the adsorption pattern on the solids studied: carbon, spinels, Sulfides, etc. The variation in $\text{Ne}\text{Ar}$ ratio may be explained by preferential diffusion of Ne. The high release temperature of meteoritic noble gases may be explained by transformation of physisorbed to chemisorbed gas, as observed in some experiments. The ready loss of meteoritic heavy gases on surficial oxidation (“Phase Q”) is consistent with adsorption, as is the high abundance. Extrapolation of the limited laboratory data suggests that the observed amounts of noble gases could have been adsorbed from a solar gas at 160–170 K and 10^?6–10^?5 atm, i.e. in the early contraction stages of the solar nebula. The principal unsolved problem is the origin of isotopically anomalous, apparently mass-fractionated noble gases in the Earth's atmosphere and in meteoritic carbon and chromite.     

Analytical electron microscopy study of the plessite structure in the Carlton iron meteorite

In order to gain a better understanding of the formation of plessite in iron meteorites, various electron optical techniques were employed to study the range of plessite structures observed in the Carlton fine octahedrite. Compositional and structural studies of twins in clear taenite and the cloudy zone were made. Transmission electron microscopy studies of martensitic and duplex α + γ plessite regions show the presence of γ-taenite rods, 10–200 nm wide, in an α-kamacite matrix. Scanning transmission electron microscope X-ray analyses showed Ni contents in the y rods of $\text{≥43}\text{wt}\text{\%}$ and Ni contents in the a matrix of 3 wt% Ni. The reaction path involves the decomposition of $\text{α}{}_2$ martensite into $\text{α + γ}$ and these reactions occur below 200°C and possibly below 100°C. Apparently the formation of plessite is intimately related to the formation of martensite and the further decomposition of martensite during the cooling history of the meteorite. It is quite probable that the martensite decomposition reaction has occurred in a large number of iron meteorites and is responsible for many of the observed plessite structures.     

Algal lipids as a possible contributor to the polymethylene chains in kerogen

Lipid fraction and cell-wall materials have been separated from three types of algae (blue green, Microcystis sp.; green, Scenedesmus sp. and diatomaceous Diatoma sp.) and their KMnO₄ oxidation products (aliphatic $\text{α,ω-C}{}_2\text{-C}{}_{12}$ dicarboxylic acids; aliphatic normal C₁₄–C₂₄ monocarboxylic acids; benzoic acid and C₁₈ isoprenoidal ketone) examined by gas chromatography and gas chromatographymass spectrometry. The results suggest that the lipid material could make a greater contribution to polymethylene chains in kerogen than the cell-wall material, when the kerogens are mainly derived from algal components.     

Transformation reactions and recycling of carotenoids and chlorins in the Peru upwelling region (15°S, 75°W)

Total chlorins and carotenoids were measured in suspended paniculate matter, sediment trap, and zooplankton fecal pellet samples collected in the Peru upwelling region. Individual carotenoids were analyzed by high pressure liquid chromatography and mass spectrometry. Fucoxanthin, diadinoxanthin, diatoxanthin, carotene, and peridinin constitute > 95% of the total carotenoid pigments in suspended paniculate matter samples. However, sediment trap and zooplankton fecal pellet samples contained significant amounts of the carotenoid transformation products fucoxanthinol, fucoxanthin 5′-dehydrate, fucoxanthinol 5′-dehydrate, peridininol and peridininol 5′-dehydrate. These samples were further characterized by high values of the ratio fucoxanthinol/total fucopigments ($\text{f/F}{}_{\mathrm{t}}$) and low values of the ratio total carotenoids /total chlorins. Three reactions are proposed to account for the formation of observed products: heterotrophic ester hydrolysis, chemically mediated epoxide rearrangement, and microbially mediated dehydration. The distribution of specific transformation products within the samples suggests that heterotrophic ester hydrolysis is a general transformation pathway operative in the water column on a wide suite of organic esters. Epoxide rearrangement and dehydration appear to occur over a longer time scale and are more typical of sedimentary environments.     

Universal stage measurements and transmission electron microscope observations of fractured plagioclase

At low to moderate temperatures of deformation, fracturing of plagioclase is common. The mechanism of fracturing is generally thought to be either a dislocation assisted process with fractures typically exhibiting some crystallographic regularity or a process of breaking along cleavage planes without the involvement of dislocations. In this study, naturally fractured plagioclase from granodiorites and a gabbro deformed at high strain rates are examined with the transmission electron microscope (TEM) to identify structures at that scale. In addition, fracture orientations are determined with the Universal stage.Some fractures observed in thin section occur parallel to (001) but many are not so simple but are confined to the [112], [1$\text{1}$2], [101], [$\text{1}$01] zones. At the TEM scale, dislocation walls or arrays are common in plagioclase. They also occupy the [101], [$\text{1}$01], [112], [1$\text{1}$2] zones. Microcracks form when dislocations are pinned in these arrays or when a free dislocation interacts with dislocations within a dislocation wall. In this way, large-scale fractures which develop inherit their crystallographic orientation from the dislocation wall.     

Light hydrocarbons in Red Sea brines and sediments

Light hydrocarbon (C₁-C₃) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 85‰}$, $\text{CH}{}_4\text{=}\text{~ 71}\text{1}$) are apparently of biogenic origin as evidenced by $\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3$) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 73‰}$, CH₄ = ~ 155 μl/l) gas seems to be of biogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~1100}$], whereas the lower brine (T = ~ 61°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 155‰}$, CH₄ = ~ 120μl/l) gas is apparently of thermogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~ 50}$]. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin.