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Die Lithogenese des Untereozäns in Nordwestdeutschland

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... They are either preserved as unconsolidated bentonites or as carbonate-cemented concretions with more or less altered glass shards (e.g. Illies 1949;Henning and Fig. 1 Palaeogeographic map of early Eocene Europe (Ziegler 1988, modified) and distribution of volcanic ashes related to the opening of the North Atlantic Ocean indicated by the main rift axis (broken line). The extension of the North Sea Basin follows Knox et al. (2010). ...
... Eocene volcanic ashes in north-western Germany were recognised and well described already in the first half of the twentieth century (Gagel 1906(Gagel , 1907(Gagel , 1910(Gagel , 1911(Gagel , 1918Gripp 1925Gripp , 1933Andersen 1938;Illies 1949). They occur in glacially dislocated or folded sequences of grey or greenish-grey clay in abandoned pits (e.g. in Niedersachsen: Basbeck, Hemmoor and Steinfeld; Schleswig-Holstein: Havighorst and Schwarzenbek), in drill cores (wells Cuxhaven 10 with 55 ash layers, Stedden, Volkensen and others) and shafts (e.g. ...
... They are mostly unconsolidated; however, a few carbonate or siderite concretions (cementstones) in close relationship to thicker ashes occur, and rarely, they are accompanied by fibrous calcite (German: Faserkalk, Danish: silkespat). Besides graded ashes with a sharp base, intercalations of ash laminae with mudstone layers occur that have to be classified as tuffites (Illies 1949). They often contain gastropods and microfossils, e.g. ...
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Unconsolidated bentonites and carbonate-cemented volcanic ashes occur in northern Germany within the clay sequence of the Lamstedt and Schlieven Formations documented by several wells. Ash-bearing carbonate concretions (so-called cementstones) are also known from glacially transported rafts and erratic boulders on the Baltic Sea island Greifswalder Oie, representing the easternmost exposures of early Eocene sediments in the North Sea Basin. The ashes can be correlated with water-lain ashes of the Danish Fur and Ølst Formations (mo-clay) generated during the opening of the North Atlantic Ocean about 55 Ma ago. Two types of cementstones can be distinguished on the basis of the mineralogical composition, sedimentary features and fossil content. Greifswalder Oie type I contains a black, up to 12-cm-thick ash deposit that follows above two distinct thin grey ash layers. The major ash unit has a rather homogeneous lower part; only a very weak normal grading and faint lamination are discernible. In the upper part, however, intercalations with light mudstone, in part intensively bioturbated, together with parallel and cross-lamination suggest reworking of the ash in a shallow marine environment. Major and trace element compositions are used to correlate type I ashes with those of the Danish-positive series which represent rather uniform ferrobasalts of the Danish stage 4, probably related to the emergence of proto-Iceland. In contrast, type II ash comprises a single, normally graded, about 5-cm-thick layer of water-lain air-fall tuff, which is embedded in fine-grained sandstone to muddy siltstone. Type II ash is characterised by very high TiO2 but low MgO contents. Exceptional REE patterns with a pronounced positive Eu anomaly suggest intense leaching of the glass that hampers exact correlation with pyroclastic deposits within the North Atlantic Igneous Province.
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Zusammenfassung: Faserkalk als Strandfund stammt meist aus glazial aufgearbeiteten Sedimenten des Eozäns (Tarras-Ton). Anstehende Vorkommen kennt man von Südholstein bis Fehmarn. Die Entstehung, Herkunft und Verbreitung sowie bekannte Farbvarianten werden kurz erläutert. Zudem werden einige besonders große Faserkalke, darunter eine Platte von 1,20 m Länge, von der Steilküste in Großenbrode / Wagrien vorgestellt.
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In der Arbeit wird ein zusammenfassender Überblick über die Ergebnisse bezüglich des Mineralbestandes unter nutzungsrelevanten Aspekten und seiner genetischen Interpretation von feinkörnigen quartären und präquartären Sedimenten Nordostdeutschlands gegeben. Zu den bearbeiteten Lagerstätten und Vorkommen zählen der Lias-Ton (Unter-Toarc) von Grimmen, Eozän-Tone (Unter- bis Ober-Eozän) und Vulkanoklastite (Unter-Eozän 1) aus Bohrungen und der Eozän-Ton (Unter-Eozän 2) der Lagerstätte Friedland, Oligozän-Tone (Mittel-Oligozän) von Jatznick und Malliß, Bändertone (Weichsel-Glazial) von Ückermünde und Möllenhagen und Geschiebemergel (Weichsel-Glazial) von Schönberg. Folgende Minerale wurden in wechselnden Mengenverhältnissen festgestellt: Montmorillonit-Muskovit-Mixed-Layer-Mineral (irregulär), Muskovit, Illit, Kaolinit, Chlorit und Glaukonit als Tonminerale i.e.S., weiterhin Quarz, Feldspat, Calcit, Dolomit, Siderit und Pyrit sowie als Sekundärminerale Halit und Sulfatminerale (wasserfrei: wie Alunit, Jarosit; wasserhaltig: wie Gips, Rozenit, Roemerit und Szomolnokit). Das Vorkommen von Montmorillonit ist auf geringmächtige bentonitisierte Vulkanoklastite des Turon, des Coniac sowie des Unter-Eozän 1 beschränkt. Das genetisch und rohstofftechnologisch wesentliche Tonmineral ist die unregelmäßige Wechsellagerung Montmorillonit-Muskovit-Mixed-Layer (innerkristallin quellfähig) mit 40 % bis 60 % montmorillonitähnlichem Schichtanteil. Der Rest hat muskovitischen Charakter. Zu den ermittelten und diskutierten nutzungsrelevanten Parametern zählen die granulometrische Zusammensetzung, das Kationenaustauschvermögen, der Durchlässigkeitsbeiwert, Wassergehalt, Trocken-, Feucht- und Proctordichte und einige rheologische Parameter wie Fließ- und Ausrollgrenze und die Plastizitätszahl. Die Meßwerte der unterschiedliche Sedimenttypen werden in Korrelation zum Mineralbestand und zur Granulometrie betrachtet. Es bestätigt sich der bekannte Einfluß der granulometrischen Zusammensetzung und der Anteil der Tonfraktion auf einen Teil dieser Parameter. Weiterhin hat einen großen Einfluß die absolute Menge des irregulären Montmorillonit-Muskovit-Mixed-Layer-Minerals innerhalb der Tonfraktion. Darüberhinaus ist zu erwarten, daß der Anteil der quellfähigen Montmorillonit-Schichtbereiche im Mixed-Layer-Mineral Bedeutung hat. Hierzu sollten noch systematische Untersuchungen erfolgen. Für die tertiären feinkörnigen Sedimente kann aus den Untersuchungen folgender genetischer Ablauf abgeleitet werden. In ein paläogeographisch begründetes marines bis flachmarines Meeresbecken im Alttertiär gelangen zwei Haupttypen von Detritus, der an der Zusammensetzung der alttertiären Sedimente beteiligt ist. Einerseits handelt es sich hauptsächlich um fluviatil und subaerisch herantransportierte Verwitterungsprodukte der oberkretazisch-tertiären Verwitterungskruste und andererseits zumindestens im Unter-Eozän 1 um subaerisch herantransportierte vulkanische Aschen. Folgende Prozesse finden statt: SEDIMENTATION von Verwitterungs-Detritus: Die detritischen Minerale sind Muskovit-Montmorillonit-Mixed-Layer (irregulär), Kaolinit, Chlorit, Muskovit, Quarz und Feldspäte. SEDIMENTATION von vulkanischen Aschen (kurzzeitig und intensiv, mehrphasig): Die Bestandteile des vulkanischen Detritus sind Sideromelan mit beginnender Palagonitisierung, Gesteinsbruchstücke (basaltisch) und Feldspäte. KOMPAKTION: Sie bewirkt mit aufsteigendem Porenwasserstrom eine Verringerung der Porosität und Permeabilität und geringfügige Veränderung in der Ionenbelegung der detritischen Minerale. Es kommt überwiegend in den Klastiten zu authigenen Neubildungen in der Altersfolge Phosphorit, Pyrit, Glaukonit, wenig Zeolithe. In den Vulkanoklastiten geht die Palagonitisierung weiter. FRÜHDIAGENESE im Klastit: Es erfolgt die Neubildung von Phosphorit, Pyrit, Glaukonit (Übergangsbereich: Kompaktion/ Frühdiagenese) und von Siderit und Calcit (dispers und Konkretionen bildend). FRÜHDIAGENESE in den Vulkanoklastiten: Sie bewirkt einerseits eine Zementation der Aschenbestandteile durch die sich neubildenden Karbonate (insbesondere Calcit und Siderit) mit Konservierung von Sideromelan, Palagonit und Gesteinsbruchstücken. Sie bewirkt andererseits im Falle einer nicht stattfindenden Zementation durch Karbonate eine Alteration der vulkanoklastischen Bestandteile zu Montmorillonit. Für den Lias-Ton von Grimmen kann ein ähnlicher Verlauf angenommen werden, ohne daß hier Vulkanoklastite auftreten. Aus den Tonmineralparagenesen der pleistozänen Sedimente kann geschlossen werden, daß ein Teil ihres Mineralbestandes infolge der glazigenen Erosion von in Hochlage befindlichen älteren Sedimenten in diese Schichtenfolge gelangte.
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Upper Cretaceous nodular limestones in Jordan were originated by burrowing organisms of the types Thalassinoides, Callianassa or Ophiomorpha. Although burrows are difficult to recognize in the pure lutitic limestones of northern Jordan, in the south they are filled by early diagenetic stochiometric dolomite or chert. One may conclude that some nodular limestones hitherto described, are products of burrowing organisms and not of purely chemical processes.
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The composition of the carbon and oxygen isotopes has been determined in about 40 carbonate concretions and surrounding clays and shales of different geological ages. Two different areas and stratigraphic levels in Northwestern Germany have been sampled: 1. concretions in shales of Lower Cretaceous age fromt he area between Hildesheim and Hannover; 2. concretions in shales of Devonian age from the Harz mountains (and the foreland). While the concretions of Group 1 generally are enriched in the light isotope 12C (δ13C values from −3.3 to −43.2‰ relative to PDB), compared to the surrounding shales (0.9 to −5.3‰), no significant differences could be observed between concretions and shales of Group 2 (concretions: 2.0 to −7.0; shales: −0.3 to −6.2). The average 18O/16O ratios of the Devonian samples are lower than those from the Cretaceous, because the probability of an exchange with “light” meteoric water in diagenetic reactions increases with geologic age. Formed under special conditions of the microenvironment, such as the presence of organic material and local alkalinity during the early stages of diagenesis, the carbon isotopic composition of concretions will probably have preserved some characteristic properties of this mioroenvironment. It is assumed that concretions with the “heavy” carbon contain carbon from CO2 which was in isotope equilibrium with CH4, both of them liberated during the decay of organic material. The “light” carbon from concretions of Group 1 is explained as fixed CO2, originating from microbiological or inorganic oxidation of organic substances, which was not in isotope equilibrium with methane (if this was present at all). After precipitation of the concretionary carbonates, no significant carbon isotope exchange seems to have occurred, otherwise the pattern of a heterogeneous carbon isotope composition found in several concretions could not be explained. Strontium concentrations (see Appendix) range from those of primary calcite precipitated in sea water to diagenetic carbonates formed from solutions with a high Ca/Sr ratio. They indicate that during the formation of concretions in abundant cases the system was closed to ocean water.
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Microprobe analyses of glass and/or minerals from 12 selected ash-layers from the lower Tertiary mo-clay (approx. 53–54 m.y.) in northern Denmark are presented. The lower part of the ash-series provides evidence of a variety of rock types including tholeiitic basalts, rhyolite, and highly differentiated peralkaline types characterized by Ti-aegirine. The upper part of the ash-series forms a homogenous population of high Fe-high Ti-low A1 tholeiites, similar to Tertiary and recent basalts from the North Atlantic province. The presence of central volcanoes and a subvolcanic complex in the source area is indicated. This, together with variations in volcanic intensity, suggests an episode of abortive spreading in the Skagerrak-North Sea area simultaneously with the early spreading in the North Atlantic Ocean.
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