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381.
Antony G. Brown Stephen Tooth Joanna E. Bullard David S. G. Thomas Richard C. Chiverrell Andrew J. Plater Julian Murton Varyl R. Thorndycraft Paolo Tarolli James Rose John Wainwright Peter Downs Rolf Aalto 《地球表面变化过程与地形》2017,42(1):71-90
The Anthropocene is proposed as a new interval of geological time in which human influence on Earth and its geological record dominates over natural processes. A major challenge in demarcating the Anthropocene is that the balance between human‐influenced and natural processes varies over spatial and temporal scales owing to the inherent variability of both human activities (as associated with culture and modes of development) and natural drivers (e.g. tectonic activity and sea level variation). Against this backdrop, we consider how geomorphology might contribute towards the Anthropocene debate by focusing on human impact on aeolian, fluvial, cryospheric and coastal process domains, and how evidence of this impact is preserved in landforms and sedimentary records. We also consider the evidence for an explicitly anthropogenic geomorphology that includes artificial slopes and other human‐created landforms. This provides the basis for discussing the theoretical and practical contributions that geomorphology can make to defining an Anthropocene stratigraphy. It is clear that the relevance of the Anthropocene concept varies considerably amongst different branches of geomorphology, depending on the history of human actions in different process domains. For example, evidence of human dominance is more widespread in fluvial and coastal records than in aeolian and cryospheric records, so geomorphologically the Anthropocene would inevitably comprise a highly diachronous lower boundary. Even to identify this lower boundary, research would need to focus on the disambiguation of human effects on geomorphological and sedimentological signatures. This would require robust data, derived from a combination of modelling and new empirical work rather than an arbitrary ‘war of possible boundaries' associated with convenient, but disputed, ‘golden’ spikes. Rather than being drawn into stratigraphical debates, the primary concern of geomorphology should be with the investigation of processes and landform development, so providing the underpinning science for the study of this time of critical geological transition. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
382.
Effects of gradient,distance, curvature and aspect on steep burned and unburned hillslope soil erosion and deposition 总被引:1,自引:0,他引:1
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Wildfire denudes vegetation and impacts chemical and physical soil properties, which can alter hillslope erosion rates. Post‐wildfire erosion can also contribute disproportionately to long‐term erosion rates and landscape evolution. Post‐fire hillslope erosion rates remain difficult to predict and document at the hillslope scale. Here we use 210Pbaex (lead‐210 mineral‐adsorbed excess) inventories to describe net sediment erosion on steep, convex hillslopes in three basins (unburned, moderately and severely burned) in mountainous central Idaho. We analyzed nearly 300 soil samples for 210Pbaex content with alpha spectrometry and related net sediment erosion to burn severity, aspect, gradient, curvature and distance from ridgetop. We also tested our data against models for advective, linear and non‐linear diffusive erosion. Statistically lower net soil losses on north‐ versus south‐facing unburned hillslopes suggest that greater vegetative cover and soil cohesion on north‐facing slopes decrease erosion. On burned hillslopes, erosion differences between aspects were less apparent and net erosion was more variable, indicating that vegetation influences erosion magnitude and fire drives erosion variability. We estimated net soil losses throughout the length of unburned hillslopes, including through a footslope transition to concave form. In contrast, on burned hillslopes, the subtle shift from convex to concave form was associated with deposition of a post‐fire erosion pulse. Such overall patterns of erosion and deposition are consistent with predictions from a non‐linear diffusion equation. This finding also suggests that concave sections of overall convex hillslopes affect post‐disturbance soil erosion and deposition. Despite these patterns, no strong relationships were evident between local net soil losses and gradient, curvature, distance from ridgetop, or erosion predicted with advection or diffusion equations. The observed relationship between gradient and erosion is therefore likely more complex or stochastic than often described theoretically, especially over relatively short timescales (60–100 years). Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
383.
Mathias Mueller Onyedika A. Igbokwe Benjamin Walter Chelsea L. Pederson Sylvia Riechelmann Detlev K. Richter Richard Albert Axel Gerdes Dieter Buhl Rolf D. Neuser Giovanni Bertotti Adrian Immenhauser 《Sedimentology》2020,67(2):849-881
Early marine diagenetic dolomite is a rather thermodynamically-stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post-depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U-Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike-slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric-preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto-Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high-grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late-stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically-complex dolomite archives must be considered with caution. 相似文献
384.
The selection criteria for the project of a new radio telescope in Egyptare described. The telescope will have a diameter of 32 m and will belocated in Abu Simbel (Upper Egypt). One major task of the telescope isthe participation in VLBI network operation. 相似文献
385.
Charles R. Stern Rolf Kilian Bettina Olker Eric H. Hauri T. Kurtis Kyser 《Lithos》1999,48(1-4):217-235
Garnet peridotite xenoliths in the Quaternary Pali-Aike alkali olivine basalts of southernmost South America are samples of the deeper portion of continental lithosphere formed by accretion along the western margin of Gondwanaland during the Phanerozoic. Core compositions of minerals in garnet peridotites indicate temperatures of 970 to 1160°C between 1.9 and 2.4 GPa, constraining a geothermal gradient which suggests a lithospheric thickness of approximately 100 km below this region. Previously, this lithosphere may have been heated and thinned to ≤80 km during the Jurassic break-up of Gondwanaland, when widespread mafic and silicic volcanism occurred in association with extension in southern South America. Subsequent cooling, by up to >175°C, and thickening, by about 20 km, of the lithosphere is reflected in low-temperature (<970°C) spinel peridotites by chemical zonation of pyroxenes involving a rimward decrease in Ca, and in moderate- and high-temperature (>970°C) peridotites by textural evidence for the transformation of spinel to garnet. A recent heating event, which probably occurred in conjunction with modal metasomatism related to the genesis of the Pali-Aike alkali olivine basalts, has again thinned the lithosphere to <100 km. Evidence for this heating is preserved in moderate- and high-temperature (>970°C) peridotites as chemical zonation of pyroxenes involving a rimward increase in Ca, and by kelyphitic rims around garnet. The majority of moderate- and high-temperature (>970°C) xenoliths are petrochemically similar to the asthenospheric source of mid-oceanic ridge basalts: fertile (>20% modal clinopyroxene and garnet), Fe-rich garnet lherzolite with major element composition similar to estimates of primitive mantle, but large-ion-lithophile and light-rare-earth element depletion relative to heavy-rare-earth elements, and with Sr, Nd, Pb, Os, and O isotopic compositions similar to MORB. In contrast, infertile, Mg-rich spinel harzburgite is predominant among low-temperature (<970°C) xenoliths. This implies a significant chemical gradient and increasing density with depth in the mantle section represented by the xenoliths, and the absence of a deep, low density, olivine-rich root below the southernmost South American crust such as has been inferred below Archean cratons. With respect to both temperature/rheology and chemistry/density, the subcontinental mantle lithosphere below southernmost South America is similar to that below oceanic crust. It is interpreted to have formed by tectonic capture, during the Paleozoic, of a segment of what had previously been oceanic lithosphere generated at a late Proterozoic mid-oceanic spreading ridge. 相似文献
386.
A method for stochastic fatigue analysis of offshore platforms is presented. The method accounts for the nonlinearity in the drag loading term, and for the systematic deviation from a Gaussian process for a platform response. The method is based on an assumed form of the stress response process at a hot spot. A number of full scale measurements for elements in fixed platforms and for marine risers show very good agreement with this assumed form. A conventional spectral fatigue approach with stochastic linearization of the drag term in the basis for the new method, which uses results from linearizations in two or more sea states. The method is easily implemented in standard computer programs presently used within the offshore oil industry for fatigue analysis. 相似文献
387.
We report on our observing programme to obtain integrated spectrophotometry, intermediate- and high-resolution major-axis
spectra, and UBR surface photometry of a representative sample of ∼ 200galaxies in the nearby field. The main goal of this programme is to
provide a comparison sample for high-redshift studies and to study the variation in star formation rates (SFRs), star formation
history (SFH),excitation, metallicity, and internal kinematics over a wide range of galaxy luminosities and morphological
types. In particular, we extend the work of Kennicutt (1992) to lower-luminosity systems. We present the main results of our
analysis so far. In these proceedings, we condense the two atlases presented of 1) images and radial surface brightness profiles
and colour profiles, and 2) images and integrated spectra into several example images, profiles and spectra, showing the general
trends observed. For the original atlases we refer the reader to the electronic distribution on CDROM or as available on the
Web at http://www.astro.rug.nl/∼nfgs/.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
388.
389.
Prof. Dr. Friedemann Freund Dipl. Min. Rolf Knobel Dr. Heinz Wengeler Dipl. Min. Hendrik Kathrein Dipl. Min. Gert Oberheuser Dr. Rainer G. Schaefer 《International Journal of Earth Sciences》1982,71(1):1-21
The recent discovery that atomic carbon occurs plentiful in olivines from mantle-derived rocks opens new aspects for the chemical evolution of the early atmosphere and the origin of life. It has been shown conclusively that atomic carbon which is dissolved in the model oxide MgO is capable of reacting in an O2-free atmosphere with the lattice oxygen to give CO2 and with the lattice hydrogen, derived from OH–, to give a profuse variety of hydrocarbons.The diffusional processes and low temperature gas/solid interface reactions involved in these processes are expected to introduce, purely abiotically, isotope fractionation resulting in a13C enrichment of the CO2 fraction and in a13C depletion of the hydrocarbon fraction which may be confused with the12C/13C isotope fractionation along biological pathways.Atomic carbon dissolved in olivines and in basalts shows a similar behaviour and yields similar quantities as C in MgO: 1–2 mg/g CO2 and 25–100g/g hydrocarbons degassing between 400 and 1000 °C. On a geological scale this means that each cubic kilometer of basaltic magma degassing in an O2-free atmosphere has the capacity of sending off about 3–6·109 kg (2·109 m3) of CO2 and about 1–3·108 kg (2·108 m3) of hydrocarbons. The presence of water modifies the composition to give, among others, alcohols and organic acids.On the basis of these results we are led to the conclusion that the early atmosphere of the earth may have contained a very high concentration of abiotically formed organic compounds of great chemical complexity.
Presented in part at the meeting Precambrian Problems, Copenhagen, March 1981. 相似文献
Zusammenfassung Die Entdeckung des atomar gelösten Kohlenstoffs in Olivinen aus Mantelgesteinen führt zu neuen Vorstellungen über die Zusammensetzung der Uratmosphäre und Entwicklungsbedingungen des Lebens. Atomarer Kohlenstoff im MgO ist in der Lage, in einer O2-freien Atmosphäre mit dem Gittersauerstoff zu CO2 zu reagieren und mit dem aus OH– stammenden Gitterwasserstoff eine große Vielfalt von organischen Verbindungen zu bilden.Diffusionsprozesse und Gas-Festkörper-Austauschreaktionen, die an diesen Reaktionen beteiligt sind, führen nach ersten Untersuchungen zu einer13C-Anreicherung im CO2 und einer13C-Abreicherung bei den Kohlenwasserstoffen. Diese12C/13C-Fraktionierung ist gleichsinnig mit der biologischen12C/13C-Fraktionierung.Atomarer Kohlenstoff in Olivinen und Basalten zeigt ein sehr ähnliches Reaktionsverhalten wie im MgO und führt zu ähnlichen Reaktionsprodukten: 1–2 mg/g CO2 und 25–100g/g Kohlenwasserstoffe zwischen 400–1000 °C. Übertragen auf geologische Verhältnisse bedeutet dies, daß jeder km3 eines entgasenden basaltischen Magmas 3–6·109 kg (2·109 m3) CO2 und 1–3·108 kg (2·108 m3) abwüschen Kohlenwasserstoff abgeben kann. Die Anwesenheit von Wasser führt zur Bildung von Alkoholen und organischen Säuren. Diese Ergebnisse deuten darauf hin, daß die Uratmosphäre und die Ursuppe viel reicher waren als bisher angenommen an komplexen organischen Verbindungen, die rein thermisch entstanden sind.
Résumé La découverte du carbone atomique dans les olivines du manteau entraîne de nouvelles idées sur la composition de l'atmosphère originelle et sur les conditions du développement de la vie. Comme l'est le cas pour le MgO, le carbone atomique dans les olivines est capable de réagir, dans une atmosphère exempte de O2, avec l'oxygène du réseau cristallin en formant du CO2, et avec l'hydrogène provenant des groupements OH– du réseau, pour former une grande variété de composés organiques.Les processus de diffusion et d'échange gas-solide liés à ces réactions provoquent, d'après les premiers résultats, un enrichissement en13C dans le CO2 et un appauvrissement en13C dans les hydrocarbures formés. Ceci ressemble au fractionnement dû à des réactions biologiques.Le comportement du carbone atomique et sa réactivité se retrouvent dans les basaltes et les olivines. La gamme des produits de réaction et leur quantité ressemble à celle du MgO: 1–2 mg/g CO2 et 25–100g/g composés organiques. A l'échelle géologique ceci implique que chaque km3 de magma basaltique dégazé en contact avec une atmosphère exempte d'oxygène pouvait émettre 3–6·109 kg, soit 2·109 m3 de CO2 et 1–3·108 kg, soit 2·108 m3 d'hydrocarbures abiotiques. La présence d'eau entraîne la formation d'alcools et d'acides organiques.La conclusion tirée de ce travail indique que l'atmosphère originelle et la»soupe primordiale» étaient plus riches qu'on ne l'a admis jusqu'à présent en composés organiques dûs à des processus purement thermiques, et donc abiotiques.
. MgO , COg, -, , . , , — — 13 2 . 12/13 , . , , - : 1–2 / O2 25–100 / , 400–1000 . , 3–6·109 (2·109 3) 2 1– 3·108 (2·108 3) . . , , , , .
Presented in part at the meeting Precambrian Problems, Copenhagen, March 1981. 相似文献
390.
Rolf Chini 《Astrophysics and Space Science》1986,128(1):217-228
Recent submm observations of dust emission from star forming regions are presented and combined with NIR and IRAS data. The spectra cover the range 0.3 to 1300 m and origin from ZAMS stars, compact Hii regions, low-luminosity objects in dark clouds and external galaxies. The dust emission spectra are interpreted in terms of density and temperature distributions around central heating sources. In addition, general properties like IR luminosity, optical depth, wavelength dependence of dust opacity and, in the case of galaxies, star formation efficiency are discussed.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献