Petrographische Untersuchungen am nordwestdeutschen Posidonienschiefer

Zusammenfassung Die vorliegende Arbeit gibt eine Beschreibung der petrographischen Verhältnisse im Posidonienschiefer. An neuen Mineralien wurden anomale zweiachsige Calcite und Whewellit festgestellt. Die Feinschichtung läßt sich nach Zählung von dickeren Lagen als Warvenschichtung erkennen. Kleine Strömungen haben Erosionsrinnen geschaffen. Von besonderem Interesse ist ein Gliederungsversuch der organischen Substanz, die sich in der differentiellen Thermoanalyse als besonders vielfältig erweist. Durch verschiedene Vorgänge bei der Diagenese wird organische durch anorganische Substanz ersetzt. Eine ganze Reihe von solchen diagenetischen Reaktionen werden beschrieben. Der stete Wechsel zwischen Sapropel—Gyttja und sogar sauerstoffreichem Wasser läßt vermuten, daß das Sediment immer wieder ein Stadium durchlief, in dem die Erdölbildung stattfinden konnte. Es kommt also als Erdölmuttergestein voraussichtlich in Frage. Weitere Untersuchungen sind abzuwarten.     

On statistical dissipation in GCM-climate

This work studies the dissipation that affects the statistical behavior of a climate variable. The hypothesis tested is that the statistical dissipation of large-scale variables in a climate model is significantly influenced by the temporal variations of the models small scale variables. The test is made with the T21 ECHAM4 atmospheric GCM by varying models representation of small-scale variables in two different ways. First, the strength of the horizontal diffusion is modified. Secondly, white noise unrelated to the state of the large-scale variables is added to variables with the smallest scales (wave numbers equal to and smaller than 18). It is found that the statistical dissipations of large-scale variables (e.g., vorticity at wave numbers equal to and larger than six) depend on the intensity of small-scale fluctuations, no matter whether they are induced by modifying the horizontal diffusion or by adding noise. The stronger the small-scale fluctuations, the stronger are the dissipations of the large-scale variables. This result suggests that the simulation of low-frequency climate variations and the prediction of climate change responses depend on the model representation of small-scale climate components.     

The determination of cloud altitudes using SCIAMACHY onboard ENVISAT

This letter shows first results for the application of a recently developed semianalytical cloud retrieval algorithm for the determination of cloud top heights from space. The technique is based on the measurements of the top-of-atmosphere reflectance in the oxygen A-band. The depth of the band depends on the cloud top height and its geometrical thickness. The data obtained are compared to ground-based measurements of the cloud top height using a cloud-profiling radar.     

A metric of background candidate assessment for spectral target signature transforms

Previous studies examined and tested a number of statistics-based registration-free transforms to find targets amid cluttered backgrounds. These transforms temporally evolve spectral target signatures under global, varying conditions using collected imagery of regions of similar objects and content distribution from datasets gathered at two different times. The transformed target signature is then inserted into the matched filter to search for targets. Although critical for transforming spectral target signatures, finding two suitable candidate regions is often difficult, computationally intensive, and may require the aid of an image analyst. This is the first study to examine a metric to help identify suitable areas for spectral target transformation. Specifically, this study examines and finds that the average correlation coefficient between the corrected histograms of the multispectral image cube collected at two times can help assess the similarity of the areas and indicate the target-to-clutter ratio, a metric shown to predict target detection performance in matched filter searches for targets.     

Chemistry, small-scale inhomogeneity, and formation of moldavites as condensates from sands vaporized by the Ries impact

The formation of the Ries impact and the moldavites have identical radiogenic ages of 14.3 Ma. According to this conformity in age moldavites are generally regarded as products of the Ries impact. This paper, which is divided into two sections, deals with two aspects of the moldavite-forming process: the formation of moldavite bodies by accretion of small precursors, and the physical and chemical conditions under which these primary units originated from sands which covered the Ries impact site.First, the chemical inhomogeneity of moldavite glasses is investigated in sections of 11 moldavites, using back scattered electron (BSE) images and electron microprobe analyses on 0.4-2.7 mm long traverses. Schlieren and lechatelierite particles are interpreted as relics of small, chemically different precursors, which accumulated to larger moldavite bodies at temperatures too low to be efficient for mixing. The patterns of schlieren and lechatelierite inclusions represent two successive rheological regimes: Small agglomerating primary melt units were extended into thin lamellae and threads under conditions of laminar flow. As evidenced by folded textures, these fluidal arrays were later plastically deformed under conditions of compressional stress.To elucidate the production of the primary melt units by the Ries impact, in the second section the geologic situation of the Ries area is considered with regard to possible source materials. The site of the Ries impact, situated at the northern border of the pre-Alpine Molasse basin, was covered at the time of the impact by fluviatile sediments of the lower sequence of the Obere Süßwasser-Molasse (OSM) Formation of Middle Miocene age, consisting of sands, marly sands and clays. Chemical analyses for major and trace elements of 38 moldavites from Bohemia and Moravia, and of 28 samples of the OSM Formation, collected from outcrops and drill holes, immediately south of the Ries crater and south of the Danube, show chemical conformity of moldavites and sand samples with regard to the major parameters SiO_2,Al₂O₃+ FeO, and MgO + CaO, indicating that these sands were the essential source material of moldavites. But, differences in contents of individual major and trace elements between moldavites and sands show that the formation of moldavites from sands involved a specific chemical differentiation which can not be explained by selective vaporization or melting, nor by selective condensation from melt or vapeur. Because large ions were enriched and small ones depleted in moldavites, the ionic radius has controlled the distribution of elements between sands and moldavites. We assume that moldavites originated from a plasma that the impact produced at its encounter with the surficial sand formation at the impact site, and that the primary units formed as early condensates in which large ions were preferentially trapped.     

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).     

A Fully Depleted pn-Junction CCD for Infrared-, UV- and X- ray detection

This paper describes the performance of the Fully Depleted pn-junction CCD (pn-CCD) system, developed for ESA's XMM-satellite mission for soft x-ray imaging and spectroscopy in the single photon counting mode in the 100 eV to 10 keV photon range. The 58 mm x 60 mm large pn-CCD array, designed and fabricated at the Semiconductor Lab (Halbleiterlabor) of the Max-Planck-Institut, uses pn-junctions for registers and as backside structure. This concept naturally enables full depletion of the detector volume independent of the silicon wafer's resistivity and thickness, and as such make it an efficient detector for the x-ray region and the infrared. For high detection efficiency in the soft x-ray region and UV, an ultrathin pn-CCD backside deadlayer has been realized. Each pn-CCD-channel is equipped with its own on-chip JFET amplifier which, in combination with the CAMEX-amplifier and multiplexing chip, facilitates parallel readout and fast data rate: the cooled pn-CCD system can be read out at a data rate up to 3 MHz with an electronic noise floor of ENC < 5 e-.     

Coupling of boundary and finite elements for soil-structure interaction problems

The investigation of complex soil-structure interaction problems is usually carried out with numerical solution procedures such as the finite element or the boundary element method. It must be noted, however, that the choice of one or the other of these approaches is not just a matter of preferences; depending on the type of the problem under consideration, either boundary or finite elements may be more advantageous. A considerable expansion in the computational power can be obtained, on the other hand, if one resorts to hybrid schemes which retain the main advantages of the two methods and eliminate their respective disadvantages. This paper presents results obtained with a boundary element-finite element coupling procedure, and discusses its applicability to some representative soil-structure interaction problems. The structures considered are elastic systems, such as foundations, tunnels and filled trenches (modelled by finite elements), which are coupled with homogeneous elastic halfspaces (modelled by boundary elements). The examples demonstrate the importance of using a model that includes wave radiation effects. The coupling approach is formulated entirely in the time domain so that an extension of the algorithm to non-linear analyses seems to present no further difficulties.     

Nd and Sr isotopes in the Aleutians: multicomponent parenthood of island-arc magmas

Young volcanic rocks from different sections of the Aleutian Islands-Alaska Peninsula Arc have been measured for ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd and some trace elements. We found the ¹⁴³Nd/¹⁴⁴Nd to be highly restricted in range ( _Nd=6 to 7) and low as compared to midocean ridge ba-salts (MORB). This indicates that the source of the Aleutian Arc magmas is different from MORB and remarkably isotopically homogeneous with respect to Nd. The range reported here for arc rocks is substantially smaller than found by other workers. However, the Sr isotope ratios vary considerably ( _Sr=–24 to –14). Those samples from small volcanic centers north of the main arc (second arc) are characterized by low _Sr. Our data in combination with previous studies suggest that there are slight geochemical differences between discrete sections of the arc. The general uniformity of Nd isotope ratios are thought to be the surface expression of an efficient mixing or homogenization process beneath the arc plate, but which still causes a wide dispersion in Sr isotopic composition.To relate the arc rocks to the broader tectonic setting and to identify possible sources of arc magmas, measurements were done on volcanic and sedimentary rocks from the North Pacific/Bering Sea area. Alkali basalts from the back-arc islands St. George, Nunivak and St. Lawrence and alkali-rich tholeiites from the fore-arc have _Nd=+4 to +9 and are correlated on the _Sr- _Nddiagram parallel to the mantle array but shifted to lower _Sr. These samples are thought to be isotopically representative of the mantle transported to that region. A tholeiitic basalt from the Kamchatka Basin ocean floor (back-arc), however, yielded typical MORB values ( _Nd=10, _Sr=–24). Composite sediment samples were made from DSDP cores in the Aleutian Abyssal Plain, Gulf of Alaska and the Alka Basin which represent mixtures of continentally and arc-derived materials. These composites have intermediate Nd isotopic ( _Nd= –2 and +2) and high Sr isotopic values ( _Sr=+9 and +37). These data show that possible source materials of the Aleutian Arc volcanics are isotopically different from and much more heterogeneous than the arc rocks themselves.On the basis of this study and of literature data, we developed a set of alternative models for volcanic arc magma generation, based on the restricted range in _Nd and the wider range in _Sr for arc rocks. Different isotopic and trace element characteristics found in different arcs or arc sections are explained by varying mixing proportions or concentrations in source materials. The basic observations require rather strict mixing ratios to obtain constant _Nd. The preferred model is one where the melting of subducted oceanic crust is controlled by the amount of trapped sediment with the melting restricted to the upper part of the altered basaltic layer. Homogenization within the upper part of the oceanic crust is brought about by hydrothermal circulation attending dewatering of the slab during subduction and possibly some oxygen exchange of the magmas on ascent.Division Contribution Number 3849 (411)     

Early Cretaceous »events« in the evolution of the eastern and western North Atlantic continental margins

At many North Atlantic continental margins, the early Neocomian is characterized by a major stratigraphic turning point from Late Jurassic-Berriasian carbonate bank/pelagic carbonate deposition to Valanginian-Barremian hemipelagic sedimentation with thick Wealden-type deltaic to deep-sea fan sequences. The stratigraphy and structure of the very old, starved passive margin of the Mazagan Plateau and adjacent steep escarpment off Morocco was studied during the French-German CYAMAZ deep diving campaign. The drowning of the Late Jurassic-early Berriasian carbonate platform was strongly influenced by a global late Berriasian sea level fall which was followed by a rapid late Valanginian sea level rise and/or by a major regional blockfaul ting event with accelerated subsidence rates. Upper Berriasian to (?) Hauterivian quartz-bearing bioclastic wackestones document the transition from the carbonate platform to the hemipelagic deposition on the drowned platform margin. Seawards, these deposits are correlated with a deep sea fan sequence. We discuss also an example from the Tarfaya Basin-Fuerteventura area further south. A 300 m thick succession of organic-rich claystone and sandstone turbidites (including m-thick debris flow units) of Hauterivian to Barremian age was an unexpected discovery at DSDP Site 603 off North Carolina (Leg 93). We discuss a tectonically confined fan model with laterally migrating channels, influenced by sea level fluctuations and varying terrigenous supply. During the Valanginian to Barremian time of high-standing (or rising) sea level, shelf construction (Wealden-type deltas) coincided with subdued, resedimentation-starved turbiditic system on the continental rise. Extensive unconsolidated sands, however, reflect sudden input of shelfal material into the basin during a mid-Aptian sea level lowstand (shelf destruction). The following global late Aptian transgression terminated the clastic fan deposition, raised the CCD and started the deposition of organic-rich shales.