Iron ore of the Lahn-Dill type formed by diagenetic seeping of pyroclastic sequences — a case study on the Schalstein section at Gänsberg (Weilburg)

Investigations on the reconstruction of processes and facies relationships from submarine volcanics of Devonian age in the Lahn syncline (Rhenish Mountains, Western Germany) reveal a complex development of secondary alteration. This is well illustrated by a mafic pyroclastic sequence (»Schalstein«) at the Gänsberg near Weilburg where alteration processes are visible by petrographic and geochemical means and can be further classified by cathodoluminescence. Iron ore formation of Lahn-Dill type is recognized as part of this alteration process, resulting from diagenetic seeping. Until recently a direct magmatic source for the Lahn-Dill type iron ore has been the generally accepted model. These bodies have therefore been viewed as a rather unique stratiform deposit, whose occurrence was virtually confined to this type area. However, it is here considered that the formation of the iron ore corresponds well with existing models of alteration processes within recent oceanic environments which are of a more universal occurrence.

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Zusammenfassung Untersuchungen zur Rekonstruktion der Abläufe an und in den submarinen Vulkangebäuden des Devons (Givet/Adorf-Phase) der Lahnmulde (südliches Rheinisches Schiefergebirge) schließen die sekundäre Alteration mit ein und werden an dem ausschließlich aus basischen Pyroklastiten (Schalstein) aufgebauten Profil am Gänsberg bei Weilburg exemplarisch vorgestellt. Diese anhand petrographischer und geochemischer Kriterien erkennbaren sekundären Prozesse zeigen eine mehrphasige Entwicklung auf, die durch Kathodenlumineszenz-Untersuchungen der Karbonatzemente bestätigt und zeitlich geordnet werden kann. Die an die pyroklastische Abfolge gebundene Roteisensteinvererzung vom Lahn-Dill-Typ läßt sich mit der bei diesen Vorgängen erfolgten Wanderung verschiedener Elemente korrelieren. Damit wird die Vererzung zu einem Produkt der diagenetischen Alteration und nicht der magmatischen Differentiation, wodurch sie mit rezent im ozeanischen Raum beobachteten Prozessen vergleichbar ist. Diese Vorstellungen fügen die Lahn-Dill-Erze in aktualistisch begründete Modelle zur Genese von Erzen ein. Damit erscheint die Besonderheit und fast nur auf den rhenoherzynischen Raum beschränkte Verbreitung dieses Typus hinfällig.

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Résumé L'étude de la succession des phénomènes et des relations facielles dans les volcanites sous-marines d'âge dévonien du synclinal de la Lahn (Massif schisteux rhénan) fait apparaître des processus complexes d'altération secondaire. Ceci est particulièrement bien illustré par la séquence pyroclastique («Schalstein») du Gänsberg près de Weilburg: les processus secondaires, identifiables par des critères pétrographiques et géochimiques y présentent un développement polyphasé dont l'histoire peut être reconstituée par application de la cathodo-luminescence au ciment carbonaté. Les minéralisations en fer associées à la série pyroclastique peuvent être corrélées avec les migrations de divers éléments impliqués dans ces processus. Ces minéralisations apparaissent ainsi comme le produit d'une altération diagénétique et ne correspondent donc pas au modèle généralement admis d'une différenciation magmatique. Cette genèse par altération est d'ailleurs conforme à ce qu'on observe dans les domaines océaniques récents de sorte que les gisements de la région Lahn-Dill doiventêtre considérés non pas comme une singularité du massif schisteux rhénan, mais comme l'expression d'un phénomène plus général à caractère actualiste.

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Hydrological and meteorological data from research catchments at the Marcell Experimental Forest,Minnesota, USA

The Marcell Experimental Forest (MEF) in northern Minnesota, USA, with hydrological research and monitoring of peatland catchments in a low-topographic relief landscape, contrasts with the mountainous terrain that typifies most research catchments. Six research catchments were instrumented and hydrological and meteorological monitoring was initiated during 1960. Paired-catchment studies, which started during 1969, have been used to assess land management and environmental change effects on forests, water availability, and biogeochemistry. Over the decades, the research and collaborations have proliferated to include new monitoring and ecosystem experiments. We provide an overview of available datasets and access information for hydrological and meteorological data. Data on streamflow, water table elevation, precipitation, snow, ground frost, air temperature, soil moisture, upland runoff, and water chemistry are discoverable with associated metadata and are archived through several Web-based, community repositories. The research programme is ongoing and we anticipate updates on an annual or more frequent basis. Additionally, we aim to release other physical, chemical, and isotopic measurements associated with long-term catchment monitoring and studies at the MEF.     

The US Gravimetric Geoid of 2009 (USGG2009): model development and evaluation

A new gravimetric geoid model, USGG2009 (see Abbreviations), has been developed for the United States and its territories including the Conterminous US (CONUS), Alaska, Hawaii, Guam, the Commonwealth of the Northern Mariana Islands, American Samoa, Puerto Rico and the US Virgin Islands. USGG2009 is based on a 1′ × 1′ gravity grid derived from the NGS surface gravity data and the DNSC08 altimetry-derived anomalies, the SRTM-DTED1 3′′ DEM for its topographic reductions, and the global geopotential model EGM08 as a reference model. USGG2009 geoid heights are compared with control values determined at 18,398 Bench Marks over CONUS, where both the ellipsoidal height above NAD 83 and the Helmert orthometric height above NAVD 88 are known. Correcting for the ellipsoidal datum difference, this permits a comparison of the geoid heights to independent data. The standard deviation of the differences is 6.3 cm in contrast to 8.4 cm for its immediate predecessor— USGG2003. To minimize the effect of long-wavelength errors that are known to exist in NAVD88, these comparisons were made on a state-by-state basis. The standard deviations of the differences range from 3–5 cm in eastern states to about 6–9 cm in the more mountainous western states. If the GPS/Bench Marks-derived geoid heights are corrected by removing a GRACE-derived estimate of the long-wavelength NAVD88 errors before the comparison, the standard deviation of their differences from USGG2009 drops to 4.3 cm nationally and 2–4 cm in eastern states and 4–8 in states with a maximum error of 26.4 cm in California and minimum of −32.1 cm in Washington. USGG2009 is also compared with geoid heights derived from 40 tide-gauges and a physical dynamic ocean topography model in the Gulf of Mexico; the mean of the differences is 3.3 cm and their standard deviation is 5.0 cm. When USGG2009-derived deflections of the vertical are compared with 3,415 observed surface astro-geodetic deflections, the standard deviation of the differences in the N–S and E–W components are 0.87′′ and 0.94′′, respectively.     

Local Ranking of Geological Conceptual Models in Non-stationary Settings Using Multi-point Geostatistics

Mathematical Geosciences - In geomodeling, it is commonly accepted that the distribution of physical properties is controlled by the architecture of geological objects. However, insufficient data...     

Bed morphology and generation of step–pool channels

Flume experiments have been carried out to study the formation processes and the bed morphology of step–pool channels. From the experiments different step types and step configurations could be distinguished depending on the stream power. These step types can be seen as an image of the generation mechanisms of step–pool systems. These results suggest that the bed roughness geometry develops towards a condition that provides the maximum possible bed stability for a given grain size distribution. In contrast to a variety of other studies, antidunes did not contribute to the generation of the step structures. However, the data of the presented study fits well into the region of antidune formation proposed by Kennedy for sand‐bed rivers. This observation points out that step–pool field‐data located in the Kennedy region do not inevitably prove that antidunes played a role in step development. It is rather proposed that in Kennedy's region of antidune formation there exist hydraulic conditions where the flow resistance is maximized. It is suggested that such maximum flow resistance is associated with an optimal distance between the bedforms and their height, independently of whether these are antidunes in sand‐ and gravel‐bed rivers or step–pool units in boulder‐bed streams. The considerations of the Kennedy region of antidune formation and the analysis of planform step types depending on stream power both suggest that steep channels have a potential for self‐stabilization by modifying the step–pool structure towards a geometry that provides maximum flow resistance and maximum bed stability. Copyright © 2008 John Wiley & Sons, Ltd.     

Non‐hyperbolic common reflection surface

The method of common reflection surface (CRS) extends conventional stacking of seismic traces over offset to multidimensional stacking over offset‐midpoint surfaces. We propose a new form of the stacking surface, derived from the analytical solution for reflection traveltime from a hyperbolic reflector. Both analytical comparisons and numerical tests show that the new approximation can be significantly more accurate than the conventional CRS approximation at large offsets or at large midpoint separations while using essentially the same parameters.     

Fluid theory with asymmetric molecular stresses: Difference between vorticity and spin equations

We present a new development in fluid theory, incorporating into it the velocity and spin fields; special attention is given to the structure of transport.The theory includes asymmetric molecular stresses and independent rotation velocity, i.e., spin. Our approach is based on our former studies on the asymmetric continuum theory with the balance and constitutive laws for displacement velocity and independent rotation motion, and points out the role of a related characteristic length unit. It is assumed that the vorticity caused by velocities can induce a spin transport counterpart. Thus, under certain conditions, an additional transport term due to rotational velocity fields may be incorporated to the velocity transport, which may lead to the vortex fields included directly into the theory.     

Stochastic models of severe weather watches and warnings: transition probabilities

To alert the public to the possibility of tornado (T), hail (H), or convective wind (C), the National Weather Service (NWS) issues watches (V) and warnings (W). There are severe thunderstorm watches (SV), tornado watches (TV), and particularly dangerous situation watches (PV); and there are severe thunderstorm warnings (SW), and tornado warnings (TW). Two stochastic models are formulated that quantify uncertainty in severe weather alarms for the purpose of making decisions: a one-stage model for deciders who respond to warnings, and a two-stage model for deciders who respond to watches and warnings. The models identify all possible sequences of watches, warnings, and events, and characterize the associated uncertainties in terms of transition probabilities. The modeling approach is demonstrated on data from the NWS Norman, Oklahoma, warning area, years 2000–2007. The major findings are these. (i) Irrespective of its official designation, every warning type {SW, TW} predicts with a significant probability every event type {T, H, C}. (ii) An ordered intersection of SW and TW, defined as reinforced warning (RW), provides additional predictive information and outperforms SW and TW. (iii) A watch rarely leads directly to an event, and most frequently is false. But a watch that precedes a warning does matter. The watch type \(\{SV\), TV, \(PV\}\) is a predictor of the warning type \(\{SW\), RW, \(TW\}\) and of the warning performance: It sharpens the false alarm rate of the warning and the predictive probability of an event, and it increases the average lead time of the warning.