ALBERT

Description: The rheology of layered meta-sedimentary rocks, and their orientation and position relative to major fault systems were the key controls on Proterozoic hydrothermal copper mineralization at Mount Isa, Australia. Compositional layering in the host rock partitioned mechanical behavior and strain, leading to selective permeability generation and the focusing of fluid flow. Shale layers preferentially failed by plastic shearing, whereas meta-siltstones remained elastic or failed in tension depending on magnitude of deformation and fluid pressure. Numerical simulations support the hypothesis that the orientation of layering and the proximity to major fault systems controlled fracturing and permeability increase in the Urquhart shale. The dilating shale provided a pathway for an upward-flowing, reduced basement fluid, from which quartz was precipitated during cooling. During a later event, the reactivation of steep structures provided access to surface derived oxidized metal-bearing brine, causing the precipitation of dolomite followed by chalcopyrite ore in the brecciated silicified shale.

Description: Recent excavations at the Eocene maar lake of Mahenge (Tanzania) by a German/Tanzanian team produced more than 1,900 fossil vertebrate, plant and trace fossils, among which fishes (51 %) make up the largest part, followed by plant remains (36 %). Surface outcrops of lacustrine sediments suggest that the Eocene crater lake was about 400 m in diameter. A 3.8 meter long section of lacustrine deposits has been documented, among which are 1.1 meter of basal lacustrine sediments that never before have been exposed. Despite intense and most probably early diagenetic dolomitization sedimentary fabrics are well preserved. Sediments from the central part of the basin are well-bedded and in places show a fine and distinctive lamination. The overall sedimentation rate in the lake centre is estimated at 0.93 mm/year. Plant fossils are characterized by an abundance of (mostly) unattached Leguminosae leaflets representing at least eight taxa out of the total of 22-23 leaf taxa distinguished so far. The Eocene vegetation at Mahenge obviously was structurally similar to the modern "miombo" woodlands of Tanzania, which are also dominated by caesalpinioid legumes. Combined with the sedimentological data, the fossil flora indicates an overall dry climate with pronounced seasonality. The Mahenge maar lake has provided five different groups of fishes plus others still undescribed. These comprise the oldest known cichlids which may represent an early species flock. Ecological requirements of the extant relatives indicate redundant evidence of the existence of a shallow water area at the lakes margins. Mammals are so far only represented by the type specimen of Tanzanycteris mannardi Gunnell et al. (2003). T. mannardi differs from all known comparable Eocene microbats in having a much larger cochlear diameter relative to basicranial width. The extremely enlarged cochlea indicates that this bat had already developed sophisticated echolocation abilities. It is possible that Tanzanycteris represents a relatively primitive ancestral rhinolophoid but the balance of its other character states aligns it with the middle Eocene Messel Hassianycteridae. Mahenge and related maar lake deposits represent a rarely sampled temporal and geographical window, which is expected to produce more significant new information about the evolution of Paleogene ecosystems in Africa, the origin of the Malagasy biota and the origin of several modern groups of plants and vertebrates, especially mammals. ---------------- German ---------------- Neue Ausgrabungen im eozänen Maarsee von Mahenge (Tansania) durch ein deutsch/tansanisches Team haben mehr als 1900 fossile Vertebraten, Pflanzen und Spurenfossilien erbracht, unter denen Fische (51 %) den größten Teil ausmachen, gefolgt von Pflanzenresten (36 %). Aufschlüsse lakustriner Sedimente belegen, dass der eozäne Kratersee ungefähr einen Durchmesser von 400 m hatte. Ein 3,8 m langes Profil in lakustrinen Sedimenten wurde dokumentiert, darunter sind 1,1 m basale lakustrine Sedimente, die noch niemals zuvor aufgeschlossen waren. Obwohl eine intensive, sehr wahrscheinlich postdiagenetische Dolomitisierung stattgefunden hat, ist das sedimentäre Gefüge gut erhalten. Sedimente aus dem zentralen Abschnitt des Beckens sind gut geschichtet und zeigen stellenweise eine feine Laminierung. Die Sedimentationsrate im Seezentrum wird auf 0,93 mm/Jahr geschätzt. Unter den pflanzlichen Fossilien sind die meist isoliert gefundenen Blattfiedern von Leguminosen am häufigsten. Sie repräsentieren mindestens acht Taxa aus der Gesamtheit von 22-23 Blatttaxa, die bislang unterschieden werden konnten. Die eozäne Vegetation von Mahenge war offensichtlich ähnlich strukturiert wie die modernen Miombowälder von Tansania, die auch von caesalpinoiden Leguminosen dominiert werden. Kombiniert mit den sedimentologischen Daten, zeigt die fossile Flora ein insgesamt trockenes Klima mit ausgeprägter Saisonalität an. Der Kratersee von Mahenge hat fünf verschiedene Gruppen von Fischen geliefert, sowie andere, die noch unbeschrieben sind. Die Fischfossilien umfassen die ältesten bekannten Cichliden, bei denen es sich um einen frühen Artenschwarm handeln könnte. Die ökologischen Anforderungen der rezenten Verwandten liefern redundante Hinweise auf die Existenz einer Flachwasserzone an den Seerändern. Säugetiere sind bislang nur durch das Typusexemplar von Tanzanycteris mannardi Gunnell et al. 2003 belegt. T. mannardi unterscheidet sich von allen bekannten vergleichbaren eozänen Kleinfledermäusen durch einen im Verhältnis zur Basicranialbreite viel größeren Durchmesser der Cochlea. Die extrem vergrößerte Cochlea belegt, dass die Fledermaus schon die komplexe Fähigkeit der Echoorientierung entwickelt hatte. Es ist möglich, dass T. mannardi eine relativ ursprüngliche Rhinolophide ist. Die Ausgewogenheit ihrer sonstigen Merkmale stellen sie jedoch in eine Reihe mit den Hassianycteridae aus dem Mitteleozän von Messel. Mahenge und assoziierte Maarseesedimente repräsentieren ein bisher selten belegtes zeitliches und geographisches Fenster, von dem weitere bedeutsame neue Informationen zur Evolution paläogener Ökosysteme in Afrika, dem Ursprung der Malagasi-Biota und dem Ursprung verschiedener moderner Gruppen von Landpflanzen und Vertebraten, insbesondere der Säugetiere, erwartet werden können.

Description: The TOR experiment (Teleseismic TOmography TORnquist) carried out in winter 1996/97 across the Trans-European Suture Zone (TESZ) in Germany, Denmark and Sweden has collected new data to investigate the transition zone between Precambrian and Palaeozoic Europe. In this study, seismograms of teleseismic earthquakes recorded by the broad-band TOR stations have been used to calculate the receiver functions. The time-domain inversion method has been applied to the receiver functions to compute S-wave velocities in the crust and uppermost mantle beneath each station. The results of inversion down to 60 km depth provide new, independent information about the distribution of S-wave velocity in this area. Beneath the Swedish stations on Baltica, the thickness of the crust varies from about 45 to 50 km with mostly gradually increasing S-wave velocity and no sharp discontinuities while for Danish and German stations the crust is thinner (29-38 km) with a sharp Moho discontinuity. A very distinct S-wave low velocity layer was found at depth of 8-16 km in the upper crust of Baltica, supported by the results of refraction/deep seismic sounding experiments using both P and S waves. The map of V p /V s ratio beneath the c. 1000 km long TOR 'profile' was obtained using the V p velocity model from previous investigations. The values of V p /V s = 1.73 were found in the uppermost crust of Baltica and upper Avalonian crust. The low velocity layer in the upper crust of Baltica is characterized by high value of V p /V s = 1.85. Relatively low S-wave velocities are observed in the lower crust of Variscides (V p /V s = 1.79), Baltica (V p /V s = 1.83) and Avalonia (V p /V s = 1.91); in the uppermost mantle V p /V s values are 1.77, 1.79 and 1.82, respectively.

Description: To mark the occasion of the 175th anniversary of the Rheinische Naturforschende Gesellschaft in 2009 and of the centennial of the Mainz Natural History Museum in 2010, we present a short account of our present knowledge of the Eckfeld Maar after 20 years of continuous research. This paper does not attempt to include all of the detailed results on the geology of the Eckfeld site or its biota. To date, nearly 250 papers and books have been published since the start of our project An up-to-date list of these publications can be found at http://www.eckfeldermaar.de.