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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.
Analysis of faulting in three-dimensional strain field 总被引：2，自引：0，他引：2
Ze'ev Reches 《Tectonophysics》1978,47(1-2)
Multiple faults, composed of three, four or more sets of faults, have been observed at a wide range of scales, from clay experiments to rift valleys. Multiple faults usually are explained by multiple phases of deformation. However, in several cases the multiple faults develop simultaneously; therefore, they cannot be explained by the common theories of faulting. Furthermore, these theories were derived for plane strain, whereas, multiple faults are associated with three-dimensional strain.An elementary analysis of faulting in three-dimensional strain field is presented here. The analysis considers the deformation of an idealized model due to slip along sets of faults; the model is subjected to strain boundary conditions. The analysis shows that (1) three or four sets of faults are necessary to accommodate three-dimensional strain, (2) there is a combination of four fault sets which minimize the dissipation of the deformation; the orientation of these faults depend on the strain state, and (3) if the resistance to slip along these four sets of faults is cohesive, then the stresses which cause slippage along them are equal or larger than the yielding stresses of a Tresca rigid-plastic with the same cohesion.The analysis presented here is too elementary to be directly applied to field observations; however, it indicates that multiple faults and rhomboid patterns of faults probably form when a body is strained three-dimensionally. 相似文献
4.
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
5.
We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth
(Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due
to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly
to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the
M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone;
(2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ
stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered
and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks
and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology,
and the host quartzites, with damage, elastic–plastic rheology. The finite-element modeling of a heterogeneous fault-zone
with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments,
as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock. 相似文献
6.
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
7.
Non-linear elastic behaviour of damaged rocks 总被引：1，自引：0，他引：1
Vladimir Lyakhovsky Ze'ev Reches Ram Weinberger Thurman E. Scott 《Geophysical Journal International》1997,130(1):157-166
The pervasive damage of rocks by microcracks and voids strongly affects their macroscopic elastic properties. To evaluate the damage effects, we derive here the macroscopic stress-strain relations for a 3-D elastic solid with non-interacting cracks embedded inside a homogeneous matrix. The cracks considered are oriented either perpendicular to the maximum tension axis, or perpendicular to the maximum compression axis. In the first case they dilate during loading and in the second case they contract during loading. We derive a solution for the elastic energy of this rock following the self-consistent scheme of Budiansky & O'Connell (1976). The solution describes the stress-strain relations in terms of Λd and μd , which are the modified Lame constants, and an additional parameter Λ. The latter accounts for the non-linear behaviour of the solid and is related to crack density. The solution predicts a non-linear elastic rheology even for an infinitesimal strain of ɛ < 0.001, and abrupt change in the elastic moduli when the loading reverses from uniaxial compression to uniaxial tension.
We use the derived solution to analyse rock-mechanics experiments in which beams of Indiana limestone were deformed under four-point loading. This configuration provides simultaneously the apparent tensile and compressive moduli for small strains. The apparent moduli fit the effective elastic moduli calculated with the present damage model well, including the differences between tensile and compressive moduli. 相似文献
We use the derived solution to analyse rock-mechanics experiments in which beams of Indiana limestone were deformed under four-point loading. This configuration provides simultaneously the apparent tensile and compressive moduli for small strains. The apparent moduli fit the effective elastic moduli calculated with the present damage model well, including the differences between tensile and compressive moduli. 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