Sediment transport in analogue flume models compared with real‐world sedimentary systems: a new look at scaling evolution of sedimentary systems in a flume     

G. POSTMA  M. G. KLEINHANS  P. TH. MEIJER  J. T. EGGENHUISEN 《Sedimentology》2008,55(6):1541-1557

Evolution of sedimentary systems at large temporal and spatial scales cannot be scaled down to laboratory dimensions by conventional hydraulic Froude scaling. Therefore, many researchers question the validity of experiments aiming to simulate this evolution. Yet, it has been shown that laboratory experiments yield stratigraphic responses to allocyclic forcing that are remarkably similar to those in real‐world prototypes, hinting at scale independency with strong dependence on boundary conditions but weak dependence on the actual sediment transport dynamics. This paper addresses the dilemma by contrasting sediment transport rules that apply in the laboratory with those that apply in real‐world geological systems. It is demonstrated that the generation of two‐dimensional stratigraphy in a flume can be simulated numerically by the non‐linear diffusion equation. Sediment transport theory is used to demonstrate that only suspension‐dominated meandering rivers should be simulated with linear diffusion. With increasing grain‐size (coarse sand to gravel) and shallowness of river systems, the prediction of long‐term transport must be simulated by non‐linear, slope‐dependent diffusion to allow for increasing transport rates and thus change in stratigraphic style. To point out these differences in stratigraphic style, three stages in infill of accommodation have been defined here: (i) a start‐up stage, when the system is prograding to base level (e.g. the shelf edge) with no sediment flux beyond the base‐level point; (ii) a fill‐up stage, when the system is further aggrading while progressively more sediment is bypassing base level with the progression of the infill; and (iii) a keep‐up stage, when more than 90% of the input is bypassing the base level and less than 10% is used for filling the accommodation. By plotting the rate of change in flux for various degrees of non‐linearity (varying the exponent in the diffusion equation) it was found that the error between model and real‐world prototype is largest for the suspension‐dominated prototypes, although never more than 30% and only at the beginning of the fill‐up stage. The error reduces to only 10% for the non‐linear sandy‐gravelly and gravelly systems. These results are very encouraging and open up ways to calibrate numerical models of sedimentary system evolution by such experiments.  相似文献   

Caldera formation on Santorini and the physiography of the islands in the late Bronze Age     

TH Druitt  V Francaviglia 《Bulletin of Volcanology》1992,54(6):484-493

The caldera of Santorini is a composite structure with a subsidence history extending over 100 ka or more. Geomorphological mapping shows that the present-day caldera wall is a complex assemblage of cliff surfaces of different ages, and that collapse at Santorini has repeatedly exhumed earlier caldera cliffs and unconformities. Cliffs bounding the southern, southeastern and northwestern rims of the caldera are morphologically fresh and probably formed during or soon after the Minoan eruption in the late Bronze Age. The well-scalloped shape of these cliffs is attributed to large-scale rotational landslip around the margins of the Minoan caldera. The deposit from one landslip is preserved subaerially. Minoan landslips in southeast santorini detached along the basement unconformity, exposing a cliff of the prevolcanic island. The caldera wall in the north, northeast and east preserves evidence for three generations of cliff: those of Minoan age and two earlier generations of caldera wall. The two early calderas can be dated relative to a well-established statigraphy of lavas and tuffs. The presence of in situ Minoan tephra plastered onto the present-day caldera wall provides evidence that these ancient caldera cliffs had already been exhumed prior to the Minoan eruption. Field relationships permit reconstruction of the physiography of Bronze-Age Santorini immediately before the Minoan eruption. The reconstruction differs from some previously published versions and is believed to be the most accurate to date. Bronze-Age Sa ntorini had a large flooded caldera formed 21 ka ago. This caldera must have acted as an excellent harbour for the Bronze-Age inhabitants of the island. The 3.6 ka Minoan eruption deepened and widened the extant caldera. The volume of Minoan collapse (25 km³) is in good agreement with published estimates for the volume of discharged magma if between 5 and 8 km³ of Minoan ignimbrite ponded as intracaldera tuff.  相似文献   

Precious metals in massive base metal sulfide deposits     

R. W. Hutchinson 《International Journal of Earth Sciences》1990,79(2):241-263

Gold and silver are ubiquitous, sometimes minor but economically important metals in massive base metal sulfide ores. Their content, proportions and distribution in the ores depend on complex, interrelated factors of their source, mobilization, transport and deposition.Different types of these deposits are formed by similar seafloor hydrothermal systems operating, however, in widely differing tectono-stratigraphic environments which span a spectrum from ensimatic-oceanic, through continent-margin to ensialic-continental ones. Like those of the base metals, the proportions and distribution of the precious metals in the ores vary regionally with these changing depositional environments. This suggests that precious metal content of the sub-seafloor rocks in which the generative fluids circulate is one factor that governs the amounts and distribution in the ores. The lithology of these source-rocks is also important. Pillowed, tholeiitic basalts have high permeability, golddepleted crystalline pillow interiors and relatively gold-rich palagonitic rims, and are consequently particularly favorable sources.Mobilization of gold from the sub-seafloor rocks may require basalt-water, and/or carbonaceous sediment-water reactions to produce strongly reduced bisulfide, carbonyl or cyanide complexes that promote gold transport. Chloride complexing and transport are less important for gold but more so for silver and the base metals.Seafloor hydrothermal discharge at shallow depth is commonly accompanied by boiling, steamblast explosions in the vent and resulting deep penetration and mixing of cool, oxygenated seawater with rising hot, reduced metalliferous fluid. This results in deposition of both chloride- and isulfide-complexed gold at depth and centrally in the footwall stockwork or in copper ore in the base of the massive body. Chloride-complexed silver, stable to lower temperatures, is carried farther and deposited with higher-level and more distal, massive zinc-lead ores. Boiling in deep water, however, although possible, is rare. This fact minimizes deep fluid mixing and allows transport of lower temperaturestable, bisulfide-complexed gold to the seafloor and outward from the vent. Gold too, is then deposited with the shallower, distal, massive zinc-lead-silver ore. Late-stage changes in fluid Eh, salinity and activity of sulfur during evolution of the generative hydrothermal system, and by discharge through previously deposited, early stage sulfides around the vent also cause diagenetic remobilization of gold, moving it to shallower, more distal locations in the system. In combination, these relationships explain the three associations of gold in primary, in-situ massive sulfide deposits; in central, deep footwall stockwork mineralization with or without copper, in central copper ore in the base of the massive body and in shallow, peripheral pyritic zinclead-silver ore.Primary, in-situ ore near the vent is sometimes reworked by seafloor density flows which transport clasts of the primary sulfides down-slope, mix them with rock and sedimentary detritus and redeposit them to form secondary, transported ore. Gold, like iron and the base metals, is diluted during this clastic transport. But silver and barite may be enriched indicating transport in the density flows not only as clasts of primary ore but partly also m solution in the hydrothermal fluids that, in this case, must have lubricated the density flows.

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Zusammenfassung Gold- und Silbervorkommen in massiven Metallsulfid-Lagerstätten sind stets ökonomisch wichtige Metalle, auch wenn sie nur in geringen Konzentrationen vorliegen. Der Gehalt an diesen Metallen und ihre Verteilung innerhalb der Lagerstätte hängt von komplexen, sich gegenseitig beeinflussenden Faktoren wie Metallquelle, Art der Mobilisation, Transport und Fällung ab.Unterschiedliche Lagerstättentypen werden von ähnlichen hydrothermalen Systemen auf den Ozeanböden gebildet. Die tektonostratigraphischen Environments unterscheiden sich dabei allerdings beträchtlich; sie befinden sich in ensimatisch-ozeanischen, kontinentalrandlichen und ensialischkontinentalen Bereichen. Innerhalb dieser regional wechselnden Ablagerungsbedingungen variiert Konzentration und Verteilung der Edelmetalle in den Lagerstätten wie bei den einfachen Metallen. Dies bedeutet, daß der Gehalt an Edelmetallen der Gesteine, die den Meeresboden unterlagern und durch die die metallhaltigen Lösungen zirkulieren, ein Faktor ist, der Menge und Verteilung der Metalle in der Lagerstätte steuert. Ebenso ist die Lithologie dieser Gesteine von Bedeutung. Als besonders gut geeignete Quellen gelten kissenartige tholeitische Basalte mit hoher Permeabilität, goldarmen Kisseninneren und relativ goldreichem palagonitischem Rand.Um das Gold aus diesen Gesteinen mobilisieren zu können, bedarf es einer Reaktion zwischen Basalt und Wasser und/oder eines karbonatischen Sediments mit Wasser, um stark reduziertes Bisulfid, Carbonyl-oder Cyanidkomplexe zu bilden, die den Goldtransport ermöglichen. Chlorid-Komplexbildung und -Transport sind zwar wichtig für Silber und einfache Metalle, für Gold spielen sie nur eine untergeordnete Rolle.Der Austritt hydrothermaler Lösungen an Ozeanböden in geringer Tiefe wird in der Regel von Sieden und explosionsartigem Dampfaustritt begleitet und führt deshalb zu einem tiefen Eindringen und Durchmischen von kaltem, sauerstoffreichen Meereswasser mit den aufsteigenden heißen, reduzierten metallischen Lösungen. Daher kommt es zur Fällung von sowohl an Chloridkomplexe als auch an Bisulfidkomplexe gebundenem Gold. Diese Ausfällung findet in größerer Tiefe statt und zwar hauptsächlich im liegenden Stockwerk oder mit Kupfer zusammen an der Basis der massiven Lagerstätte. An Chloridkomplexe gebundenes Silber ist auch bei niedrigeren Temperaturen stabil, wird also weiter transportiert und in einem höheren Niveau in distal gelegenen Blei-Zink-Lagerstätten gefällt. In größeren Wassertiefen kommt es seltener zu dem beobachteten Sieden der austretenden Lösungen. Diese Tatsache reduziert das Durchmischen der Lösungen in größeren Tiefen und ermöglicht den Transport von Gold, das an Bisulfidkomplexe gebunden ist. In diesem Fall ist die Verbindung auch bei niedrigeren Temperaturen noch stabil also transportfähig und kann bis zum Meeresboden oder außerhalb des Schlotes in Lösung bleiben. Dabei kann das Gold zusammen mit Blei, Zink und Silber in mehr distalen Lagerstätten angereichert werden. Späte Änderungen in Eh, Salinität und Schwefelaktivität der Lösungen während der Entwicklung des hydrothermalen Systems, sowie der Austritt durch früher abgelagerte den Schlot umgebende Sulfide, können eine diagenetische Gold-Remobilisation auslösen. Auch dabei kann das Metall zu in geringer Tiefe liegenden, distalen Ablagerungsorten transportiert werden. Berücksichtigt man alle Faktoren, so erklären diese Verhältnisse die drei möglichen Goldvorkommen in primären, in-situ vorliegenden Sulfid-Lagerstätten: Mit Kupfer vergesellschaftet, allerdings nicht unbedingt, zentral im liegenden Stockwerk; an der Basis der Kupferlagerstätte und in geringer Tiefe in Verbindung mit peripheren Blei-Zink-Silber-Vorkommen.Primäre, in-situ neben Schloten vorkommende Lagerstätten werden in einigen Fällen von meeresbodennahen Masseströmen aufgearbeitet. Diese transportieren Sulfidkomponenten, die während des Transports mit Sediment und Gesteinsbruchstücken vermischt und schließlich als sekundäre sedimentäre Lagerstätte abgelagert werden. Durch diesen Transport und die Mischung der Klastika wird die Goldkonzentration in der späteren Lagerstätte stark reduziert. Silber und Barit können dagegen in Ausnahmefällen während des Transports angereichert werden, da diese Komponenten nicht nur als Sulfidbruchstücke transportiert werden, sondern auch in Lösung in den hydrothermalen Lösungen vorhanden sein können. Diese Lösungen dienen in solchen Fällen den Masseströmen als Gleithorizont.

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Résumé Dans les gisements de sulfures métalliques massifs, l'or et l'argent sont des métaux ubiquistes, parfois mineurs, mais toujours d'importance économique. Leur teneur et leur distribution dans les corps minéralisés dépendent de facteurs complexes, en relation les uns avec les autres, tels que: leur source, leur mobilité, leurs modalités de transport et de dépôt.A partir des mêmes systèmes hydrothermaux en action sur le fond de la mer, divers types de gisements peuvent être engendrés, selon leur environnement tectono-stratigraphique: océanique ensimatique, de marge continentale ou continental ensialique. Les teneurs et la répartition des métaux précieux, comme celle des autres métaux varient régionalement selon ces divers milieux. Ceci suggère que le contenu en métaux précieux dans les roches sous-jacentes au fond marin à travers lesquelles circulent les solutions minéralisantes est un facteur qui détermine leurs teneurs et leurs répartitions dans les minerais. La lithologie de ces roches-sources est également importante. Une source particulièrement significative est représentée par les coussins des basaltes tholéiitiques, très perméables, avec leur coeur pauvre en or et leur couronne palagonitique relativement riche.Le lessivage de l'or dans les roches situées sous le fond marin peut impliquer des réactions eau-basalte et/ou eausédiments carbonatés, réactions susceptibles d'engendrer les bisulfures très réduits et les complexes carbonés ou cyanurés qui permettent le transport de l'or. Le transport par complexes chlorurés joue un rôle subordoné dans le cas de l'or, mais important dans le cas de l'argent et des autres métaux.L'arrivée de solutions hydrothermales sur les fonds marins peu profonds est d'ordinaire accompagnée d'ébullitons et d'émissions explosives de vapeur, ce qui provoque la pénétration profonde d'eau de mer froide et oxygénée et son mélange avec les fluides métallifères chauds et réducteurs ascendants. Il en résulte le dépôt de complexes aurifères bisulfurés et chlorurés. Cette précipitation s'opère en profondeur, particulièrement dans les roches sous-jacentes ou dans le minerai de cuivre, à la base des corps minéralisés massifs. L'argent des complexes chlorurés, stables à plus basse température, est transporté plus loin et se dépose, en situation plus distale, dans les minerals massifs de Pb-Zn. Dans les mers profondes, l'ébullition, sans être impossible, est néanmoins un phénomène rare; cette circonstance minimise le mélange des fluides en profondeur et permet le transport de l'or jusqu'à la surface du fond et même loin des évents sous la forme de complexes bisulfurés stables à basse température. L'or est alors déposé en situation distale peu profonde avec les minerals massifs de Zn-Pb-Ag. Des modifications tardives d'Eh, de salinité et d'activité du soufre dans les solutions au cours de l'évolution du système hydrothermal, de même que le lessivage des sulfures déjà accumulés autour des évents entraînent une remobilisation diagénétique de l'or vers des situations distales d'eau peu profonde. La combinaison de ces divers facteurs permet d'expliquer les trois occurrences de l'or dans les dépôts in situ de sulfures massifs primaires: dans les parties centrales des masses sous-jacentes en association ou non avec le Cu, à la base des corps minéralisés en Cu, et à faible profondeur, en liaison avec les gisements périphériques de Pb-Zn-Ag.Les gisements primaires, formés in situ près des évents sont parfois remaniés par des courants de densité, qui emportent des clastes de sulfures, les mélangent aux débris sédimentaires et les redéposent sous forme de minerais secondaires. De tels transports provoquent la dilution de l'or, en même temps que celle du fer et des autres métaux. Par contre, l'argent et la barite peuvent subir un enrichissement car leur transport dans les courants de densité ne s'effectue pas seulement sous forme de clastes, mais également en solution dans des fludies hydrothermaux, lesquels, dans ce cas, contribuent à lubrifier le courant de densité.

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Column Amounts of ClONO2, HCl, HNO3, and HF from Ground-Based FTIR Measurements Made Near Kiruna, Sweden, in Late Winter 1994     

TH. Blumenstock  H. Fisher  A. Friedle  F. Hase  P. Thomas 《Journal of Atmospheric Chemistry》1997,26(3):311-321

During SESAME phase I ground-based FTIR measurements were performed atEsrange near Kiruna, Sweden, from 28 January to 26 March 1994. Zenith columnamounts of ClONO₂, HCl, HF, HNO₃,O₃, N₂O, CH₄, and CFC-12 werederived from solar absorption spectra. Time series of ClONO₂and HCl indicate a chlorine activation at the end of January and around 1March. On 1 March a very low amount of HCl of 2.09times; 10¹⁵molec. cm^-2 was detected, probably caused by a second chlorineactivation phase starting from an already decreased amount of HCl. The ratioof column amounts of HCl to ClONO₂ decreased inside the vortexfrom about 1 in January to 0.4 in late March compared to values of about 2outside the vortex. Although the Arctic stratosphere was rather warm in winter1993/94 and PSCs occurred seldom, chlorine partitioning into its reservoirspecies HCl and ClONO₂ changed during that winter andClONO₂ is the major chlorine reservoir at the end of thewinter as in cold winters like 1991/92 and 1994/95.  相似文献   

The Sahelian desertification debate: a view from the American south-west     

Charles F. Hutchinson 《Journal of Arid Environments》1996,33(4):519-524

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Marine and limnic radiocarbon reservoir corrections for studies of late- and postglacial environments in Georgia Basin and Puget Lowland, British Columbia, Canada and Washington, USA     

Ian Hutchinson  Thomas S. James  Brian D. Bornhold 《Quaternary Research》2004,61(2):193-203

Models of late-glacial environmental change in coastal areas are commonly based on radiocarbon ages on marine shell and basal lake sediments, both of which may be compromised by reservoir effects. The magnitude of the oceanic reservoir age in the inland waters of the Georgia Basin and Puget Lowland of northwestern North America is inferred from radiocarbon ages on shell-wood pairs in Saanich Inlet and previously published estimates. The weighted mean oceanic reservoir correction in the early and mid Holocene is −720±90 yr, slightly smaller than, but not significantly different from, the modern value. The correction in late-glacial time is −950±50 yr. Valley-head sites yield higher reservoir values (−1200±130 yr) immediately after deglaciation. The magnitude of the gyttja reservoir effect is inferred from pairs of bulk gyttja and plant macrofossil ages from four lakes in the region. Incorporation of old carbon into basal gyttja yields ages from bulk samples that are initially about 600 yr too old. The reservoir age declines to less than 100 yr after the first millennium of lake development. When these corrections are accounted for, dates of deglaciation and late-glacial sea-level change in the study area are pushed forward in time by more than 500 yr.  相似文献   

A catalogue of major and trace element data for Icelandic Holocene silicic tephra layers     

RH. H. Meara  TH. Thordarson  N. J. G. Pearce  C. Hayward  G. Larsen 《第四纪科学杂志》2020,35(1-2):122-142

Tephra layers with Icelandic provenance have been identified across the North Atlantic region in terrestrial, lacustrine, marine and glacial environments. These tephra layers are used as marker horizons in tephrochronology including climate studies, archaeology and environmental change. The major element chemistries of 19 proximally deposited Holocene Icelandic silicic tephra layers confirm that individual volcanic systems have unique geochemical signatures and that eruptions from the same system can often be distinguished. In addition, glass trace element chemistry highlights subtle geochemical variations between tephra layers which appear to have identical major element chemistry and thus allows for the identification of some, if not all, tephra layers previously considered identical in composition. This paper catalogues the compositional variation between the widespread Holocene Icelandic silicic tephra deposits.  相似文献   

An analysis of failure mechanism constraints on pre-failure rock block deformation using TLS and roto-translation methods     

Emily Rowe  D. Jean Hutchinson  Ryan A. Kromer 《Landslides》2018,15(3):409-421

Rockfall hazards increase the risk of train derailment along railway corridors in western Canada. In this study, repeated terrestrial laser scanning (TLS) datasets were collected every 2–3 months at three different sites along the Thompson and Fraser River corridors in British Columbia, referred to as the Goldpan, White Canyon, and Mile 109 sites. A total of 207 rockfall events occurring across all three sites between November 11, 2014 and October 18, 2016 were recorded in a database. For each of these rockfalls, pre-failure deformation was measured using a method of three-dimensional roto-translation block tracking. Each rockfall was classified by its deformation behaviour and further categorised based on failure mechanism, volume, lithology, and the roughness condition of the failure plane. Results reveal that detectable levels of deformation were measured in 33% of the total number of rockfall events using the present methods. Rotation deformation was most commonly observed in toppling failures with relatively steep joint orientations. Conversely, planar sliding blocks generally exhibited the least measurable deformation, with the majority not showing any precursory translation or rotation. It is postulated that overhanging rockfall configurations may suppress the expression of deformation in rockfall source blocks, though additional research is required to confirm this.  相似文献   

ATTENUATION OF RANDOM NOISE BY 2-D AND 3-D CDP STACKING AND KIRCHHOFF MIGRATION*     

TH.C. KREY 《Geophysical Prospecting》1987,35(2):135-147

Three-dimensional seismic surveys, in general, do not need the same high degree of CDP coverage as 2-D surveys to achieve a certain signal-to-noise ratio after migration. This can be shown theoretically for Kirchhoff migration and laterally uncorrelated noise. More precisely, there exists a formal relationship between the multiplicity of CDP coverage of a 3-D survey and that of a 2-D survey with the same signal-to-uncorrelated-noise ratio. Frequency and aperture are parameters in the corresponding expression. Heuristically the relationship can be obtained by applying the concept of the Fresnel zone. Though the mathematics in this paper refer to laterally uncorrelated noise, the underlying concepts can probably also be used for weakly correlated noise, e.g., for multiple reflections and for the low-frequency remnants of surface waves.  相似文献   

Geochemistry of waters in the Valley of Ten Thousand Smokes region, Alaska     

T.E.C. Keith  J.M. Thompson  R.A. Hutchinson  L.D. White 《Journal of Volcanology and Geothermal Research》1992,49(3-4)

Meteoric waters from cold springs and streams outside of the 1912 eruptive deposits filling the Valley of Ten Thousand Smokes (VTTS) and in the upper parts of the two major rivers draining the 1912 deposits have similar chemical trends. Thermal springs issue in the mid-valley area along a 300-m lateral section of ash-flow tuff, and range in temperature from 21 to 29.8°C in early summer and from 15 to 17°C in mid-summer. Concentrations of major and minor chemical constituents in the thermal waters are nearly identical regardless of temperature. Waters in the downvalley parts of the rivers draining the 1912 deposits are mainly mixtures of cold meteoric waters and thermal waters of which the mid-valley thermal spring waters are representative. The weathering reactions of cold waters with the 1912 deposits appear to have stabilized and add only subordinate amounts of chemical constituents to the rivers relative to those contributed by the thermal waters. Isotopic data indicate that the mid-valley thermal spring waters are meteoric, but data is inconclusive regarding the heat source. The thermal waters could be either from a shallow part of a hydrothermal system beneath the 1912 vent region or from an incompletely cooled, welded tuff lens deep in the 1912 ash-flow sheet of the upper River Lethe area.Bicarbonate-sulfate waters resulting from interaction of near-surface waters and the cooling 1953–1968 southwest Trident plug issue from thermal springs south of Katmai Pass and near Mageik Creek, although the Mageik Creek spring waters are from a well-established, more deeply circulating hydrothermal system. Katmai caldera lake waters are a result of acid gases from vigorous drowned fumaroles dissolving in lake waters composed of snowmelt and precipitation.  相似文献