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1.
International Journal of Earth Sciences - The end-Cretaceous biological crisis is represented by the demise of the non-avian dinosaurs. However, most crucial biologically was the elimination of the... 相似文献
2.
Experimental study on metallation of tetrapyrroles in biphasic systems showed that complexation with metal cations of the first transition series is a feasible under chemical environments similar to the naturally occurring ones. The metal transport from the aqueous media to the organic, which is a novel approach using naturally occurring fatty acids hydroxy aromatic compounds and thiols, is demonstrated. Selectivity between Ni2+ and VO2+ complexation is achieved under sulfurous rich conditions. The kinetic implications are discussed in view of their geoenvironmental applicability. 相似文献
3.
The decomposition of palmitic (C16), stearic (C18) and behenic (C22) acids with and without montmorillonite was studied in an inert atmosphere under isothermal (250 C) “bulk flow” conditions, using a CDS-820ZA automated pyro-analyser. The C8C21 hydrocarbons and the CO2 evolved were determined. It appears that in this open system montmorillonite affected the retention time of the acids and hence the kinetics of the reactions rather than the nature of the hydrocarbons formed. The reaction kinetics were very sensitive to changes in experimental conditions.The rate of hydrocarbon formation depended on the chain length of the carboxylic acid. In the absence of montmorillonite palmitic acid tended to sublimate before appreciable amounts of hydrocarbons were formed, stearic acid decomposed to give a range of n alkanes and alkanes while behenic acid yielded only very minor amounts of hydrocarbons. The presence of montmorillonite retarded hydrocarbon evolution with stearic acid. The hydrocarbon with one carbon atom less than the parent acid predominated in all one hour runs and the yield was increased by the presence of montmorillonite. The amount of CO2 evolved never exceeded 10% of the maximum possible. It appears that the reaction mechanism is complex with several processes occurring concurrently. 相似文献
4.
Fifteen sediment samples were studied from five drill sites recovered by the ‘Glomar Challenger’ on Legs I and IV in the Gulf of Mexico and western Atlantic. This study concentrated on compounds derived from biogenic precursors, namely: (1) hydrocarbons, (2) fatty acids, (3) pigments and (4) amino acids.Carbon isotope (δC13) data (values < ? 26%, relative to PDB), long-chain n-alkyl hydrocarbons ( ?C277) with odd carbon numbered molecules dominating even carbon numbered species, and presence of perylene proved useful as possible indicators for terrigenous contributions to the organic matter in some samples. Apparently land-derived organic matter can be transported for distances over 1000 km into the ocean and their source still recognized.The study was primarily designed to investigate: (i) the sources of the organic matter present in the sediment, (ii) their stability with time of accumulation and (iii) the conditions necessary for in situ formation of new compounds. 相似文献
5.
Z. Aizenshtat 《Geochimica et cosmochimica acta》1973,37(3):559-567
Perylene was found in a variety of marine sediments, in a shale and in peat. It is suggested that its precursors arise predominantly from land organisms and are carried into oceanic traps along with detrital minerals. When rates of deposition are fast, and reducing conditions are established within the sediment, biogenic pigment precursors of perylene are converted to the polycyclic aromatic hydrocarbon, which is then stabilized by π-bonding with metals and protected from degradation. 相似文献
6.
Reduced sulfur species were studied to constrain isotopic exchange-mixing with synthetic polysulfide cross-linked macromolecules (PCLM), model sulfur containing molecules and natural sulfur-rich kerogen, asphalt and oil of the Dead Sea area. PCLM represents protokerogens that are rich in sulfur and thermally unstable. Mixing rates of PCLM with (added as (NH4)2S(aq)) at low to moderate temperatures (50-200 °C) are rapid. Elemental sulfur and H2S(gas) fully mix isotopes with PCLM during pyrolysis conditions at 200 °C. During these reactions significant structural changes of the PCLM occur to form polysulfide dimers, thiolanes and thiophenes. As pyrolysis temperatures or reaction times increase, the PCLM thermal products are transformed to more aromatic sulfur compounds. Isotopic mixing rates increase with increasing pyrolysis temperature and time. Polysulfide bonds (S-S) in the PCLM are responsible for most of these structural and isotopic changes because of their low stability. Conversely, sulfur isotope mixing does not occur between dibenzothiophene (aromatic S) or hexadecanthiol (C-SH) and at 200 °C after 48 h. This shows that rates of sulfur isotope mixing are strongly dependent on the functionality of the sulfur in the organic matter. The order of isotopic mixing rates for organic matter is kerogen > asphalt > oil, which is inverse to their sulfur thermal stability. Asphalt and oil with more refractory sulfur show significantly lower isotopes mixing rates than the kerogen with more labile sulfur. Based on the findings of the present study we suggest that sulfur isotopes mixing can occur from early diagenesis into catagenesis and result in isotopic homogenization of the inorganic and organic reduced sulfur pools. 相似文献
7.
Zeev Lewy 《Geoarchaeology》2006,21(2):187-196
The Zedekiah Cave is situated within an area of ancient limestone quarries. The quarried tunnel system extends more than 200 m from the small entrance. Important reasons must have prompted the transition to technically complicated subsurface activity. Quarrying proceeded mainly along a single layer of porous bioclastic limestone. The fresh, wet rock is friable, easily cut and carved. When exposed and dried, the blocks become casehardened from the periphery inward. Such rock was needed for renovation of the Second Temple under the religious restrictions that no iron (metal) tool should be used at the holy site, and these blocks could be finally shaped with nonmetallic tools. These unique geological and religious factors resulted in the subsurface quarrying of the building stones. Hence, the Zedekiah Cave was dug some 565 years after King Zedekiah allegedly fled through the cave out of Jerusalem to Jericho where the Babylonian soldiers captured him. © 2006 Wiley Periodicals, Inc. 相似文献
8.
Zeev Arad 《Journal of Arid Environments》1993,24(4)
We compared water relations and resistance to desiccation in three sympatric desert land snails, Eremina desertorum, Euchondrus desertorum and Euchondrus albulus. Ermina was the most resistant and Eu. albulus the least resistant to desiccation. Juveniles of both Euchondrus species were more susceptible to desiccation than adults. The rate of mass loss, during desiccation, of Eremina is comparable to values previously measured in other desert species. Its resistance to desiccation may be correlated with its more exposed micro-habitat (it lives on bushes) and/or with its Saharan origin. On the other hand, Euchondrus is an under-stone dweller of a northern origin and thus has an almost Mediterranean-type water economy. 相似文献
9.
Organic sulfur in marine sediment is 34S enriched relative to the co-existing pyrite. This phenomenon is still enigmatic. Timing of the sulfur incorporation, immobilization and different sulfur species involved are part of the explanations. The reduced sulfur species incorporation into organic matter (OM) is generally assumed to have negligible δ34S fractionation. This assumption has never been confirmed by laboratory experimental data. The present study measures the δ34S changes resulting from reduced sulfur species (sulfides and polysulfide anions) incorporation into organic model compounds in an aquatic and low temperature (25 °C) system that simulates diagenetic marine environment. In addition, we also investigate the δ34S fractionation and the isotope chemical mixing in the formation of polysulfide anions produced from elemental sulfur and sulfide anions. The results showed total isotope mixing between the two species in the formation of polysulfides. Acidification of the polysulfides solution caused δ34S fractionation between the released elemental sulfur and H2S. The incorporation of polysulfides and sulfides into carbonyl groups, caused 34S enrichment relative to the starting polysulfides and sulfide of 4–5‰. The 34S enrichment of the sulfurized carbonyl groups showed a minimal effect by temperature (0–70 °C) and is not affected by salinity, polysulfides composition, reaction time or solubility in water. The incorporation of polysulfides and sulfides into brominated organic compounds was negligibly 34S enriched. The chemical mechanisms controlling the polysulfides incorporation into OM depend mostly on the functional groups and determine the 34S enrichment of the sulfurized OM. The results presented in this study can explain part of the difference between pyrite δ34S and sulfurized OM δ34S in natural marine sediments. 相似文献
10.
Hydrous pyrolysis experiments at 200 to 365°C were carried out on a thermally immature organic-rich limestone containing Type-IIS kerogen from the Ghareb Limestone in North Negev, Israel. This work focuses on the thermal behavior of both organic and inorganic sulfur species and the partitioning of their stable sulfur isotopes among organic and inorganic phases generated during hydrous pyrolyses. Most of the sulfur in the rock (85%) is organic sulfur. The most dominant sulfur transformation is cleavage of organic-bound sulfur to form H2S(gas). Up to 70% of this organic sulfur is released as H2S(gas) that is isotopically lighter than the sulfur in the kerogen. Organic sulfur is enriched by up to 2‰ in 34S during thermal maturation compared with the initial δ34S values. The δ34S values of the three main organic fractions (kerogen, bitumen and expelled oil) are within 1‰ of one another. No thermochemical sulfate reduction or sulfate formation was observed during the experiments. The early released sulfur reacted with available iron to form secondary pyrite and is the most 34S depleted phase, which is 21‰ lighter than the bulk organic sulfur. The large isotopic fractionation for the early formed H2S is a result of the system not being in equilibrium. As partial pressure of H2S(gas) increases, retro reactions with the organic sulfur in the closed system may cause isotope exchange and isotopic homogenization. Part of the δ34S-enriched secondary pyrite decomposes above 300°C resulting in a corresponding decrease in the δ34S of the remaining pyrite. These results are relevant to interpreting thermal maturation processes and their effect on kerogen-oil-H2S-pyrite correlations. In particular, the use of pyrite-kerogen δ34S relations in reconstructing diagenetic conditions of thermally mature rocks is questionable because formation of secondary pyrite during thermal maturation can mask the isotopic signature and quantity of the original diagenetic pyrite. The main transformations of kerogen to bitumen and bitumen to oil can be recorded by using both sulfur content and δ34S of each phase including the H2S(gas). H2S generated in association with oil should be isotopically lighter or similar to oil. It is concluded that small isotopic differentiation obtained between organic and inorganic sulfur species suggests closed-system conditions. Conversely, open-system conditions may cause significant isotopic discrimination between the oil and its source kerogen. The magnitude of this discrimination is suggested to be highly dependent on the availability of iron in a source rock resulting in secondary formation of pyrite. 相似文献