06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
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Item Open Access "A la recherche du temps perdu" : on geological condensation, with examples from the Jurassic Subbetic Plateau in Southeastern Spain(1993) Fels, Alexander; Seyfried, HartmutEine kondensierte Ablagerung ist eine marine Rückstandsbildung, die sich autochthon und kontinuierlich über einen längeren Zeitraum hinweg gebildet hat. Kondensation kann synsedimentar durch Abschirmung, Ablenkung oder Abtragung von Schlamm erfolgen; diagenetisch läuft Kondensation vor allem über Bioerosion auf Hartboden in Verbindung mit unterschiedlich tiefgreifender Erosion ab. Im Jura des subbetischen Plateaus (früher "externes Subbetikum") wird das Umkippen in eine Kondensations-Situation durch tektonische Bewegungen gesteuert, indem benachbarte Plattformen den Export von Schlamm selbssteuernd regulieren. Das subbetische Plateau durchlief vier Phasen stark reduzierter Sedimentation: Carixien - Unter-Domerien(Kondensatlonsepisode 1), Obertoarcien - Unter-Bajocien (Kondensationsepisode 2), Unterbathonien - Unter-Oxfordien (Kondensationsepisode 3) und unterstes Kimmeridgien (Kondensationsepisode 4). Hartboden, die sich während dieser Episoden bildeten, sind meistens von Goethitkrusten und Goethitonkoiden bedeckt. Die meisten Goethitkrusten bestehen entweder aus sehr dünnen (20 - 50 p.) Laminae mit krümeligem und pseudofilamentösem Gefüge, die für einen mikrobiellen Ursprung der Krusten sprechen, oder sie bestehen aus strukturlosem, "sterilen" Goethiterz. Aus einer Abschätzung der Wachstumsraten folgern wir, daß der überwiegende Teil der Zeit, die in solchen Krusten versteckt ist, entweder im nur wenige Milimeter dicken Goethiterz dokumentlert ist oder in Hartböden bzw. Erosionsflächen gelöscht wurde. Kondensierte Abfolgen zelgen meistens eine hierarchische Gliederung in Sequenzen, die vom Meter- bis zum Millimeterbereich reichen und nahezu stets denselben Aufbau haben: sie beginnen mit reduzierter Sedimentation, auf die ein Omissionsstadium folgt und schließen melstens mlt Goethitkrusten ab. Unter den vielen Faktoren, die für eine solche Abfolge verantwortlich sein konnen, kristallisiert sich als kleinster gemeinsamer Nenner ein (nicht eindeutig kalibrierbares) eustatisches Signal heraus. Wir betrachten deshalb kondensierte Sequenzen, die Goethitkrusten enthalten, als pelagische Parasequenzen.Item Open Access Theoretische Untersuchungen der stationären Rotorblattumströmung mit Hilfe eines Euler-Verfahrens(1991) Krämer, EwaldDie vorliegende Arbeit beschreibt die Entwicklung eines numerischen Verfahrens zur Berechnung der aerodynamischen Umströmung eines Hubschrauberrotorblattes auf der Basis der Eulerschen Bewegungsgleichungen. Besonderes Merkmal des Verfahrens ist die Tatsache, daß der von dem betrachteten Blatt generierte Nachlauf, der einen entscheidenden Einfluß auf die Strömungsverhältnisse vor dem nachfolgenden Blatt hat (Blatt-Nachlauf-lnterferenz), nicht durch ein Wirbelmodell vorgegeben, sondern als Teil der Lösung berechnet wird ("Wake-Capturing"). Bei dem verwendeten impliziten Lösungsalgorithmus handelt es sich um eine Finite-Volumen-Methode unter Verwendung eines Upwind-Schemas höherer Ordnung. Der Lösungsweg basiert auf der Charakteristikenmethode für hyperbolische Gleichungssysteme. Im Ergebnisteil der Arbeit werden die Resultate einer Reihe von Berechnungen für einen zweiblättrigen Modellrotor dargestellt und mit experimentellen Meßdaten sowie mit Ergebnissen anderer theoretischer Methoden verglichen. Daneben liegt ein Schwerpunkt der Arbeit auf der Darstellung des berechneten Nachlaufes in verschiedenen Referenzebenen zwischen den Rotorblättern sowie auf der Wiedergabe seiner zeitlichen Entwicklung (Anfahrvorgang).Item Open Access Stratigraphic chart of the sedimentary basins of Costa Rica, Central America(1994) Sprechmann, Peter; Astorga, Allan; Calvo, Claudio; Fernández, AlbertoCosta Rican sedimentary rocks deposited since the Campanian are subdivided into supergroups, groups, subgroups, and formations. The Curime, Boruca and Cerece supergroups are unconformity-bounded units. The preexisting number of formations is considerably reduced. The remaining rock units described in this paper are defined by their depositional environment, using differential sedimentologic criteria. The use of sequence stratigraphic terminology is discussed.Item Open Access Der älteste kalkalkaline Inselbogen-Vulkanismus in Costa Rica. Marine Pyroklastika der Formation Loma Chumico (Alb bis Campan)(1994) Calvo, Claudio; Bolz, AngelaIn diesem Artikel werden die ältesten vulkanischen Produkte des Costa-Rica-Inselbogens untersucht, die Subduktions-Prozesse am westlichen Rand der Karibischen-Platte in der Unter-Kreide belegen.Item Open Access Depositional sequences and sequence boundaries in fore-arc coastal embayments : case histories from Central America(1991) Schmidt, Hannelore; Seyfried, HartmutFrom Oligocene to Recent times a series of tectonically controlled coastal embayments formed on the Pacific fore-arc side of the southern Central American island-arc system. Each of these basins shows characteristic stratal geometries and facies distributions reflecting the complex interaction of changes of sea level, volcaniclastic input, and tectonic activity (subsidence, uplift). Sequential stratigraphic correlations based on sequence analysis and discontinuity surfaces indicate that eustatic sea-level changes control architecture, geometry, and facies distribution of depositional sequences at the level of second-order cycles. Owing to the particular tectonic position, complete sets of systems tracts are seldom developed. Voluminous sediment supply, especially during episodes of strong volcanic activity, may overcompensate transgressions. Strong uplift may annihilate any sedimentary documentation or reduce sequences to a strongly condensed package with random preservation of estuarine or deltaic facies. The bounding uncomformities (sequence boundaries) are traceable on a regional scale and are related at the level of second-order sequence boundaries to tectonic events that repeatedly affected the island arc during the episode in question.Item Open Access Kretazische Subduktionsprozesse in Südzentralamerika(1998) Calvo, Claudio; Seyfried, Hartmut (Prof. Dr.)The study presents a combined sedimentological, micropaleontological and petrological approach to the Cretaceous sedimentary basement and cover sequences of the Costa Rican arc orogen. The findings show an evolved volcanic arc with explosive calc-alkaline volcanism, which was active since at least the Albian. This intraoceanic arc was built on the western Caribbean Plate boundary where the oceanic Farallon Plate was continuously subducting. Some evidence suggests that the subduction processes in southern Central America might have already begun in the Late Jurassic.Item Open Access Sea level change : a philosophical approach(1993) Leinfelder, Reinhold; Seyfried, HartmutThe present Cenozoic era is an lsquoicehousersquo episode characterized by a low sea level. Since the beginning of the industrial revolution, the human race has been emitting greenhouse gases, increasing the global atmospheric temperature, and causing a rise in sea level. If emissions continue to increase at the present rate, average global temperatures may rise by 1.5°C by the year 2050, accompanied by a rise of about 30 cm in sea level. However, the prediction of future climatic conditions and sea level is hampered by the difficulty in modelling the interactions between the lithosphere, kryosphere, biosphere and atmosphere; in addition, the buffering capacity of our planet is still poorly understood. As scientists cannot offer unambiguous answers to simple questions, sorcerer's apprentices fill in the gaps, presenting plans to save planet without inconveniencing us. The geological record can help us to learn about the regulation mechanisms of our planet, many of which are connected with or expressed as sea level changes. Global changes in sea level are either tectono-eustatic or glacioeustatic. Plate tectonic processes strongly control sea levels and climate in the long term. There is a strong feed-back mechanism between sea level and climate; both can influence and determine each other. Although high sea levels are a powerful climatic buffer, falling sea levels accelerate climatic accentuation, the growth of the polar ice caps and will hence amplify the drop in sea level. Important sources of fossil greenhouse gases are botanic CO2 production, CO2 released by volcanic activity, and water vapour. The latter is particularly important when the surface area of the sea increases during a rise in sea level (lsquomaritime greenhouse effectrsquo). A lsquovolcanogenic greenhouse effectrsquo (release of volcanogenic CO2) is possibly not equally important, as intense volcanic activity may take place both during icehouse episodes as well as during greenhouse episodes. The hydrosphere, land vegetation and carbonate platforms are major CO2 buffers which may both take up and release CO2. CO2 can be released from the ocean due to changes in the pCO2 caused by growth of coral reefs and by uptake of CO2-rich freshwater from karst provinces. Efficient sinks of CO2 are the weathering products of silicate rocks; long-term sinks are organic deposits caused by regional anoxic events which preferrably develop during sea level rises and highstands; and coal-bearing strata. Deposition of limestone also removes CO2 from the atmospheric-hydrospheric cycle at a long term. Biotic crises are often related to either sea-level lows or sea-level highs. Long-term sea-level lows, characteristic of glacial periods, indicate cooling as major cause of extinction. During verly long-lasting greenhouse episodes the sea level is very high, climate and circulation systems are stable and biotic crises often develop as a consequence of oxygen depletion. On land, niche-splitting, complex food web structures and general overspecialization of biota will occur. Whether the crisis is caused by a single anoxic event (e.g. in the Late Devonian) or a disturbance by an asteroid impact (e.g. the Cretaceous/Tertiary boundary), it will only trigger total collapse of an ecosystem if a large part of it was already in decline. The regulatory mechanisms and buffers are thermodynamically extremely efficient if they are given sufficient time in which to deploy their power. However, after major catastrophes the re-establishment of successful ecosystems will take millions of years. The present rate of sea level and associated temperature rise is much too fast to be compensated and buffered by the network of natural controls. It is likely that the transitional time towards a new steady state will be an extremely variable and chaotic episode of unpredictable duration.Item Open Access Response of deep-water fore-arc systems to sea-level changes, tectonic activity and volcaniclastic input in Central America(1991) Winsemann, Jutta; Seyfried, HartmutThe incipient island-arc system of southern Central America (Cretaceous - early Oligocene) is characterized by thick turbidite systems, which mainly filled inner fore-arc troughs. Outcrop data show four second-order depositional sequences in the deep-water sediments. The formation of these depositional sequences is strongly related to the morphotectonic evolution of the island-arc system. Each depositional sequence reflects the complex interaction between global sea-level fluctuations, sediment supply and tectonic activity. Strong marginal uplift and high volcaniclastic sediment supply during early to late Paleocene and late Eocene times caused the formation of coarse-grained channel-lobe systems. During late Paleocene and mid-Eocene times, fine-grained, thin-bedded turbidite systems were deposited, owing to regional subsidence and a decrease in volcanic supply. Uplift and subsidence of sediment-source areas acted as major controls on deposition of basinal cycles.Item Open Access An innovative algorithm to accurately solve the Euler equations for rotary wing flow(1992) Wagner, Siegfried; Krämer, EwaldDue to the ability of Euler methods to treat rotational, nonisentropic flows and also to correctly transport on the rotation embedded in the flow field it is possible to correctly represent the inflow conditions on the blade in the stationary hovering flight of a helicopter, which are significantly influenced by the tip vortices (blade-vortex interaction) of all blades. It is shown that also the very complex starting procedure of a helicopter rotor can be very well described by a simple Euler method that is to say without a wake model. The algorithm based on the procedure is part of category upwind schemes, in which the difference formation orientates to the actual, local flow state that is to say to the typical distrubance expansion direction. Hence, the artificial dissipation required for the numerical stability is included in a natural way adapted to the real flow state over the break-up error of the difference equation and has not to be included from outside. This makes the procedure robust. An implicit solution algorithm is used, where the invertation of the coefficient matrix is carried out by means of a Point-Gauss-Seidel relaxation.Item Open Access Anatomy of an evolving island arc : tectonic and eustatic control in the south Central American fore-arc area(1991) Seyfried, Hartmut; Astorga, Allan; Ammann, Hubert; Calvo, Claudio; Kolb, Wolfgang; Schmidt, Hannelore; Winsemann, JuttaThe southern part of the Central American isthmus is the product of an island arc. It evolved initially as a ridge of primitive island-arc tholeiites at a collision zone between the Farallon plate and proto-Caribbean crust (Albian-Santonian). During the Campanian, a major tectonic event (most probably subduction reversal) caused décollement of different units of the former plate margin. The resulting structural high was covered by a carbonate platform. From Maastrichtian to Eocenc times continuous subduction produced a stable morphotectonic configuration (trench-slope-outer-arc-fore-arccalcalkaline-arc). Fore-arc sedimentation was controlled by volcaniclastic input and tectonic activity along the outer arc's inner margin. Eustatic control is essentially recognized through lowstand signals such as extensive turbidite sand lobes. Steady accretionary uplift of the outer arc gradually closed the bypasses between forc-arc and trench slope. Eustatic control is verified by lowstand signals (sands) on the trench slope and highstand signals on the outer arc (carbonate ramps). During the Oligocene another major tectonic event affected the entire system: accretion ceased, segments decoupled, and regional compression resulted in general uplift and erosion. From latest Oligocene to Pliocene times, three episodes of tilting created a series of fault-angle depressions. Subsidence varies enormously among these basins. but sedimentation is largely shallow marine. Facies architecture reflects complex interactions between tectonic processes, changes in volcaniclastic sediment supply, and eustasy. Subsequently. very strong explosive volcanic activity resulted in excessive sediment input that overfilled most basins. The history of the island arc shows that tectonic processes largely controlled composition, distribution and geometry of the major sedimentary units. Eustatic signals do indeed occur when they are expected, but may be considered as an overprint rather than a dominating factor.