Radish concretions grown in mud during compaction

Radish concretions exhibit a typical columnar to pear-shaped, stipe down-ward geometry. In Middle Jurassic mudrock in south-west Germany, radish concretions started to form around an iron-sulphide lined tube by pervasive cementation constituting an ellipsoidal parent domain in uncompacted sediment at burial depths of ≤5 to 8 m as recorded by 75 to 80% minus-cement porosity. Thereafter, the concretions grew vertically in compacting sediment as evidenced by laminae within the concretions being increasingly inclined towards the tips, and concomitantly decreasing minus-cement porosity. During early diagenesis, prior to septarian crack formation, bicarbonate generating the microbial cement originated within the sulphate reduction zone chiefly from anaerobic oxidation of methane and to a lesser degree of organo-clastic material. Later, at 50 to 70 m burial depth, septarian cracks formed as evaluated by sedimentation-compaction analysis based on minus-cement porosity data and compressibility of similarly composed sediments. The outward-narrowing septarian cracks indicate that they formed when the con- cretions were still in a plastic state but already cemented sufficiently to be resistant against compaction. In this stage, up to one-quarter of the pore vol- ume of the concretions was still open as suggested by shrinkage experi- ments. This pore volume, and the septarian cracks, were filled with cement termed late diagenetic. In the study area, the decompacted net-sedimentation rate was low, about 2 to 3 cm kyr −1 , for ca 2.5 Myr, allowing the concretions to reside for a long time within the sulphate reduction zone and to grow. Radish concretions formed within the transition zone from thick, rapidly deposited to long-term, slowly accumulating sediment

Two-dimensional finite element models of convective heat transfer in the upper crust — implications for the interpretation of fission-track data

Fission-track (FT) thermochronology is a tool routinely used for studies of surface denudation because of its sensitivity to the low temperatures found in the uppermost part of the crust. FT ages and associated track length distributions are regularly interpreted assuming a steady-state temperature field and only conductive heat transfer. However, application of the method to thermochronological studies based on such interpretations may lead to invalid conclusions, if the temperatures at a certain depth had actually varied with time. For example, the convective transfer of heat by hydrothermal fluids can cause transient thermal events within the upper crust. In particular, fluid circulation along fault zones can result in substantial convective heat transport and cause temperature anomalies in the adjacent rocks (Zuther & Brockamp 1988, Fleming et al. 1998, Lampe & Person 2002, Bächler et al 2003). As a consequence, any refined interpretation of FT data requires a thorough understanding of the upper crustal temperature field and its evolution through time. The main objective of this study is to assess quantitatively how convective heat transport influences the upper crustal temperature field as well as the cooling ages and track length distributions observed in apatite FT data...conferenc

First record of the leptonectid ichthyosaur Eurhinosaurus longirostris from the Early Jurassic of Switzerland and its stratigraphic framework

An incomplete skull of the leptonectid ichthyosaur Eurhinosaurus longirostris found in the Rietheim Member (previously "Posidonienschiefer”; Toarcian, Early Jurassic) of Staffelegg, Canton Aargau, is the first record from Switzerland of this taxon and supports the status of Eurhinosaurus longirostris as a palaeobiogeographic very widespread ichthyosaur species in the Early Toarcian of Western Europe. Being from either the Bifrons or Variabilis zone, it is one of the youngest records of Eurhinosaurus and one of the few diagnostic ichthyosaur finds from this time interval. The partial skull is well articulated and preserved three-dimensionally in a carbonate concretion. Both the mode of preservation of the ichthyosaur and an associated ammonoid (Catacoeloceras raquinianum) provided the age of the concretion, which had been collected from scree. Taphocoenosis and taphonomy show the C. raquinianum to be one of few non re-worked fossils recorded from the Early to Late Toarcian boundary (Bifrons/Variabilis zone) of northern Switzerland in general and of this ammonite species in particular. The Toarcian section at Staffelegg differs from other localities where strata of the same age are exposed with respect to facies variations of the Rietheim Member (previously "Posidonienschiefer”, Early Toarcian) and the extraordinarily high thickness of the Gross Wolf Member (previously "Jurensis-Mergel”, Late Toarcian

Überörtliche Biotopverbundplanungen : eine planerische Grundlage für den Straßenbau

Anhand von drei OU im Zuge von Bundesstraßen wird dargestellt, wie die überörtliche Biotopverbundplanung dazu beitragen kann, Eingriffe nicht nur punktuell-lokal, sondern im größeren Zusammenhang der Biotopverbundsysteme zu bewerten und zu bewältigen. Die Biotopverbundplanung stellt einen Ideen- und Flächenpool bereit, Maßnahmen aus nicht ausgleichbaren Eingriffen sinnvoll zu konzentrieren und mit bestmöglicher Wirkung für Natur und Landschaft umzusetzen. Die Straßenbauverwaltung greift die Vorschläge der Biotopverbundplanung gern auf, wie weitere, bereits realisierte Vorhaben zeigen. Allerdings darf man nicht übersehen, dass Kompensationsmaßnahmen für Eingriffe an anderer Stelle bestenfalls dazu beitragen, die Qualität der Biotopverbundsysteme auf dem gegenwärtigen Stand zu erhalten

A calibrated composite section for the Late Jurassic Reuchenette Formation in northwestern Switzerland (?Oxfordian, Kimmeridgian sensu gallico , Ajoie-Region)

Abstract.: A new stratigraphical frame for Kimmeridgian sediments of northwestern Switzerland has been established by correlating seventeen closely spaced sections by means of lithological, sedimentological, and microfacial data as well as by ammonites. This newly established stratigraphical frame is of great value, because these sediments are usually characterised by a prominent sparseness of index-fossils (i.e. ammonites). The biostratigraphical frame is based on seven species of ammonites and corroborated by ostracodes. The investigated sedimentary record is divided into nine intervals and assigned to the Late Oxfordian to Late Kimmeridgian sensu gallico (middle Eudoxus-Zone). Exact lithological correlations between the outcrops are achieved by three marker beds. The new stratigraphical frame is a pre-requirement for refining correlations of sections, for reconstructing sea level fluctuations, and for quantifying synsedimentary differential subsidenc

Graben width controlling syn-rift sedimentation: the Palaeogene southern Upper Rhine Graben as an example

Eocene to Early Oligocene syn-rift deposits of the southern Upper Rhine Graben (URG) accumulated in restricted environments. Sedimentation was controlled by local clastic supply from the graben flanks, as well as by strong intra-basinal variations in accommodation space due to differential tectonic subsidence, that in turn led to pronounced lateral variations in depositional environment. Three large-scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions. They form three major base level cycles that can be traced throughout the basin, each of them representing a stratigraphic sub-unit. A relatively constant amount of horizontal extension (ΔL) in the range of 4-5km has been estimated for the URG from numerous cross-sections. The width of the rift (L f ), however, varies between 35 and more than 60km, resulting in a variable crustal stretching factor between the bounding masterfaults. Apart from block tilting, tectonic subsidence was, therefore, largely controlled by changes in the initial rift width (L 0). The along-strike variations of the graben width are responsible for the development of a deep, trough-like evaporite basin (Potash Basin) in the narrowest part of the southern URG, adjacent to shallow areas in the wider parts of the rift such as the Colmar Swell in the north and the Rhine Bresse Transfer Zone that delimits the URG to the south. Under a constant amount of extension, the along-strike variation in rift width is the principal factor controlling depo-centre development in extensional basin

Experimental determination of the glass transition temperature in a very narrow temperature range by Temperature Modulated Optical Refractometry

Latest since the landmark studies of Kovacs and co-workers on the glass transition of polymers, it is clear that thermally induced volume changes are of central importance for the understanding of the nature of the glass transition. Due to the kinetic background of the canonical (thermal) glass transition, it does not seem possible to derive a well-defined glass transition temperature T_g based on susceptibilities such as the thermal volume expansion coefficient, \beta(T), being strongly coupled to the glass transition process. Therefore, in practice, T_g is for example defined via the inflection point of the step-like \beta(T) curve. In this publication, we propose to use a thermo-optical feature, preceding the glass transition in the high-temperature phase, to determine the glass transition temperature T_g of a model polymer in a rather narrow temperature interval.Comment: Preprin

Dynamic environmental conditions recorded by the trace fossil Teichichnus and event beds during deposition of the basal Vaca Muerta Formation in the central Neuqu´en Basin (Argentina)

The mud-dominated part of the basal Vaca Muerta Formation in the central Neuquén Basin accumulated mainly under dysoxic conditions as indicated by the absence of both fine lamination and large burrows, typical of anoxic and oxic conditions, respectively. Event beds and large, strata-bound concretions preserving a nearly uncompacted sediment fabric document rather discontinuous deposition, in particular as concretions must reside within the zone of carbonate supersaturation for a prolonged period of time to form. The mudrock hosts numerous ash layers. Among them is a bed up to 40 cm-thick that was deposited by storm-induced currents and later became calcified. It contains abundant, winding Teichichnus up to 220 cm-long. The trace producers partly reworked their own spreite and probably applied a gardening and sequestrichnial nutritional strategy (that is collecting and stowing of nutritional material in the burrow for later utilization). The spreite fill documents depositional processes that delivered argillaceous sediment and provided oxygen. The ash originally constituting the Teichichnus bed originated from the volcanic arc west of the basin. In contrast, the erosive surface limiting the Teichichnus bed is covered by mud, implying sediment delivery from the east or south where rivers entered the basin while the climate was (at least seasonally) humid, whereas aridity increased towards the north. Consequently, an estuarine circulation likely developed and prevailed during the initial transgression of the lower Vaca Muerta Formation while cold Palaeo-Pacific water flowed into the subsiding and expanding basin. Later, during prevailing dry climate, an anti-estuarine circulation was probably established

Trackway of a disabled seabird

An uncommon trackway of a seabird consisting of impressions of the right foot accompanied at the left side at the supposed position of the foot only by holes was produced by a gull having two legs, but only one foot. Foot size and stride are typical of an adult herring gull. The stride is unequal between right-left and left-right impression by ~15% as the digitigrade producer experienced re-distribution of load due to the missing foot. Tracks of disabled seabirds are underrepresented in reports of both modern settings as well as the fossil record when compared with modern observations. In present time, about 2% of the seabirds have injured feet or legs. Today, however, injuries of seabirds might have increased due to human fishery activities. Actual observations show that fossilisation of such trackways is favoured by microbes preferentially growing in the impressions that are moist for a prolonged period of time

A large skull of Ichthyosaurus (Reptilia: Ichthyosauria) from the Lower Sinemurian (Lower Jurassic) of Frick (NW Switzerland)

An incomplete skull of an ichthyosaur attributed to Ichthyosaurus communis Conybeare 1822 is reported from the Lower Sinemurian calcarenites (upper part of the "Beggingen Member”, previously "Arietenkalk”, Semicostatum zone) of Frick (Canton Aargau, northern Switzerland). It is the first record of this genus and species in Switzerland, and the first definite record of the genus Ichthyosaurus from central Europe. This species was hitherto only known from Lower Hettangian to Lower Sinemurian deposits of England and Upper Sinemurian sediments of Belgium. The specimen represents a particularly large individual that considerably exceeds all known English representatives of this species in skull length, and is closest in size to the single specimen from Belgium. Unusual anatomical features include a strong coossification of the posterior skull-roof bones (probably a result of an old ontogenetic age) and a very elongate and deep excavatio internasalis. A short overview of substantial Swiss Mesozoic ichthyosaur finds is provided. The Jurassic record appears very patchy so far, but has been considerably improved thanks to recent discoverie