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  • 1
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    Gravity changes from a stress evolution earthquake simulation of California (2006)
    In:  J. Geophys. Res., Oxford and Edinburgh, Blackwell Scientific Publications, vol. 111, no. B9, pp. 1-14, pp. B09408, (ISBN: 0534351875, 2nd edition)
    Details
    Publication Date: 2006
    Description: The gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks. A stress evolution time-dependent model was used to create simulated slip histories over the San Andreas Fault network in California. Using a linear sum of the gravity signals from each fault segment in the model, via coseismic gravity Green's functions, a time-dependent gravity model was created. The steady state gravity from the long-term plate motion generates a signal over 5 years with magnitudes of ...
    Keywords: Gravimetry, Gravitation ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Stress ; Strain ; Modelling ; 1217 ; Geodesy ; and ; Gravity: ; Time ; variable ; gravity ; 7209 ; Seismology: ; Earthquake ; dynamics ; 0515 ; Computational ; Geophysics: ; Cellular ; automata ; 4430 ; Nonlinear ; Geophysics: ; Complex ; systems ; Fernandez
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    ASTRONAUTICS INFORMATION. ELECTRICALLY PROPELLED SPACECRAFT AND ASSOCIATED SUBJECTS (1962)
    In:  CASI
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    Publication Date: 2008-08-25
    Description: Astronautics information. electrically propelled spacecraft
    Keywords: PHYSICS, PLASMA
    Type: JPLAI/LS-428
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  • 3
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    Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The organic matter found in sedimentary rocks must derive from many sources; not only from ancient primary producers but also from consumers and secondary producers. In all of these organisms, isotope effects can affect the abundance and distribution of 13C in metabolites. Here, by using an improved form of a previously described technique in which the effluent of a gas chromatograph is continuously analysed isotopically, we report evidence of the diverse origins of sedimentary organic matter. The record of 13C abundances in sedimentary carbonate and total organic carbon can be interpreted in terms of variations in the global carbon cycle. Our results demonstrate, however, that isotope variations within sedimentary organic mixtures substantially exceed those observed between samples of total organic carbon. Resolution of isotope variations at the molecular level offers a new and convenient means of refining views both of localized palaeoenvironments and of control mechanisms within the global carbon cycle.
    Keywords: Exobiology
    Type: Nature (ISSN 0028-0836); Volume 343; 6255; 254-6
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  • 4
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    Evidence for only minor contributions from bacteria to sedimentary organic carbon (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Because their molecular signatures are often prominent in extracts of sediments, bacteria are thought to be important contributors to petroleum source beds. It has been shown recently, however, that abundances of biomarkers do not always reflect relative contributions to sedimentary organic carbon (Corg). The contribution of photosynthetic green sulphur bacteria to sediments can be assessed effectively because the diagenetic products of distinctive carotenoids from these organisms occur widely and their biomass is isotopically labelled, being enriched in 13C. We show here that, although sediments and oils from the Western Canada and Williston basins contain prominent biomarkers of photosynthetic bacteria, the absence of 13C enrichment in the total Corg requires that the bacterial contribution is in fact minimal. Although the importance of bacterial reworking of sedimentary debris cannot be doubted, we argue that our findings, when considered in conjunction with those from other settings, suggest that bacterial biomass may commonly represent only a minor component of total Corg in carbonaceous rocks.
    Keywords: Exobiology
    Type: Nature (ISSN 0028-0836); Volume 369; 224-7
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  • 5
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    Carbon isotope evidence for the stepwise oxidation of the Proterozoic environment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The oxidation of the earth's crust and the increase in atmospheric oxygen early in earth history have been linked to the accumulation of reduced carbon in sedimentary rocks. Trends in the carbon isotope composition of sedimentary organic carbon and carbonate show that during the Proterozoic aeon (2.5-0.54 Gyr ago) the organic carbon reservoir grew in size, relative to the carbonate reservoir. This increase, and the concomitant release of oxidizing power in the environment, occurred mostly during episodes of global rifting and orogeny.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6396; p. 605-609.
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  • 6
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    A 6,000-year sedimentary molecular record of chemocline excursions in the Black Sea (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Black Sea is the world's largest anoxic basin; it is also a contemporary analogue of the environment in which carbonaceous shales and petroleum source beds formed. Recently, Repeta et al. reported that anoxygenic photosynthesis may be an important component of carbon cycling in the present Black Sea, owing to a shoaling of the chemocline and consequent penetration of the photic zone by anaerobic waters in the past few decades. It has been suggested that this was due to an anthropogenic decrease in freshwater input to the Black Sea, although natural causes were not ruled out. Here we report the distributions of sequestered photosynthetic pigments in eight core samples of sediments from the Black Sea ranging in age from zero to 6,200 years before the present. Our results show that photosynthetic green sulphur bacteria (Chlorobiaceae [correction of Clorobiaceae]) have been active in the Black Sea for substantial periods of time in the past. This finding indicates that the penetration of the photic zone by anaerobic waters is not a recent phenomenon, and suggests that natural causes for shoaling of the chemocline are more likely than anthropogenic ones.
    Keywords: Life Sciences (General)
    Type: Nature (ISSN 0028-0836); Volume 362; 6423; 827-9
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  • 7
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    Terminal Proterozoic reorganization of biogeochemical cycles (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Proterozoic aeon (2,500-540 million years ago) saw episodic increases in atmospheric oxygen content, the evolution of multicellular life and, at its close, an enormous radiation of animal diversity. These profound biological and environmental changes must have been linked, but the underlying mechanisms have been obscure. Here we show that hydrocarbons extracted from Proterozoic sediments in several locations worldwide are derived mainly from bacteria or other heterotrophs rather than from photosynthetic organisms. Biodegradation of algal products in sedimenting matter was therefore unusually complete, indicating that organic material was extensively reworked as it sank slowly through the water column. We propose that a significant proportion of this reworking will have been mediated by sulphate-reducing bacteria, forming sulphide. The production of sulphide and consumption of oxygen near the ocean surface will have inhibited transport of O2 to the deep ocean. We find that preservation of algal-lipid skeletons improves at the beginning of the Cambrian, reflecting the increase in transport by rapidly sinking faecal pellets. We suggest that this rapid removal of organic matter will have increased oxygenation of surface waters, leading to a descent of the O2-sulphide interface to the sea floor and to marked changes in the marine environment, ultimately contributing to the Cambrian radiation.
    Keywords: Geosciences (General)
    Type: Nature (ISSN 0028-0836); Volume 376; 6535; 53-6
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  • 8
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    The combined application of organic sulphur and isotope geochemistry to assess multiple sources of palaeobiochemicals with identical carbon skeletons (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Five immature sediments from a Messinian evaporitic basin, representing one evaporitic cycle, were studied using molecular organic sulphur and isotope geochemistry. It is shown that a specific carbon skeleton which is present in different "modes of occurrence" ("free" hydrocarbon, alkylthiophene, alkylthiolane, alkyldithiane, alkylthiane, and sulphur-bound in macromolecules) may have different biosynthetic precursors which are possibly derived from different biota. It is demonstrated that the mode of occurrence and the carbon isotopic composition of a sedimentary lipid can be used to "reconstruct" its biochemical precursor. This novel approach of recognition of the suite of palaeobiochemicals present during the time of deposition allows for identification of the biological sources with an unprecedented specificity.
    Keywords: Geosciences (General)
    Type: Organic geochemistry (ISSN 0146-6380); Volume 19; 4-6; 403-19
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  • 9
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    Origin of petroporphyrins. 2. Evidence from stable carbon isotopes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Compared with the carbon-13 isotopic composition of the ubiquitous C32DPEP (DPEP, deoxophylloerythroetioporphyrin) the heavy but equivalent carbon-13 isotopic composition for the porphyrin structures 15(2)-methyl-15,17-ethano-17-nor-H-C30DPEP and 15,17-butano-, 13,15-ethano-13(2),17-propano-, and 13(1)-methyl-13,15-ethano-13(2),17-propanoporphyrin suggests a common precursor, presumably chlorophyll c, for these petroporphyrins isolated from the marine Julia Creek oil shale and the lacustrine Condor oil shale. Similarly, the heavy but variable carbon-13 isotopic composition of 7-nor-H-C31DPEP compared with C32DPEP is consistent with an origin from both chlorophyll b and chlorophyll c3. The equivalent carbon-13 isotopic composition for 13(2)-methyl-C33DPEP compared with C32DPEP suggests a common origin resulting from a weighted average of chlorophyll inputs.
    Keywords: Exobiology
    Type: Energy & fuels : an American Chemical Society journal (ISSN 0887-0624); Volume 4; 6; 658-61
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  • 10
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    Molecular palaeontological evidence for food-web relationships (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors present evidence of organic compounds derived from insect waxes from sediments of the lagoonal and sabkha sedimentary systems of the coast of Abu Dhabi.
    Keywords: Exobiology
    Type: Die Naturwissenschaften (ISSN 0028-1042); Volume 81; 128-30
    Format: text
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