Eberhard Schindler

Event-stratigraphic markers within the Kellwasser crisis near the Frasnian/Famennian boundary (upper Devonian) in Germany

Abstract Short time intervals of anomalous conditions, often referred to as “global events”, yield excellent tools for detailed stratigraphic correlations. In addition to pronounced effects minor features may be applied for fine-scale comparisons of rock sequences. These include alternations within a given portion of rock, or distinct layers at exactly the same position; such marker horizons are often traceable over long distances. Recognition of these specific markers allows for a more detailed search for possible causes of anomalous events.

Magnetostratigraphy susceptibility of the Frasnian/Famennian boundary

Magnetosusceptibility event and cyclostratigraphy (MSEC) is used to establish a non-polarity-based magnetostratigraphy susceptibility (MSS) between the stratotype region for the Frasnian/Famennian (F/F) boundary sequence in the Montagne Noire of southern France, the eastern Rheinisches Schiefergebirge of Germany, Belgium, the eastern Anti-Atlas of Morocco, and the Arbuckle Mountains of southern Oklahoma (USA). Despite differences of depositional environment, the MSS is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the Montagne Noire reference section. The nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated MSZ1, MSZ2, MSZ3, MSZ4, MSZ5, MSZ6, and MSZ7. These are characterized in terms of the magnitude of their duration. The MSS reference section of choice for the F/F boundary is the well-known Trench C at La Serre (LSC) in the northeastern Montagne Noire of southern France. The F/F boundary is located at the lower boundary of magnetozone La Serre Iα3b at La Serre as well as in all other sections studied. MSZ4 and MSZ5 magnetozones are used to establish intra- and inter-regional correlation between the reference sequence and the other regions. The base of the Upper Kellwasser event is as variable within the MSS zonation as it is within the biostratigraphic zonation, as is the position of the Lower Kellwasser event.

MID-PALEOZOIC TRILOBITE LAGERSTÄTTEN: MODELS OF DIAGENETICALLY ENHANCED OBRUTION DEPOSITS

Abstract Spectacular trilobite Lagerstätten occur in distinctive offshore calcareous mudstone facies through the Late Ordovician to Devonian, and reflect a combination of mass mortality or molting and burial, coupled with early diagenetic enhancement. Evidence indicates two distinct modes of burial, Type I and II assemblages, which show evidence for burial without or with seafloor disturbance, respectively. Type I assemblages suggest rapid (hours to days), but not instantaneous burial, without bottom disruption, enabling preservation of in situ behavior, including mass aggregations and molt ensembles. Most occurrences contain bedding planes in which trilobites exhibit incipient disarticulation. These assemblages were buried by cascades of flocculated sediment from hypopycnal, detached flows. Type II assemblages show well-articulated, enrolled, semi-enrolled, and outstretched trilobites in varied orientations relative to bedding. In such cases, bottom flows and seafloor disruption by storm or seismic disturbances in shallow waters suspended large amounts of flocculated muds as viscous slurries, which developed into hyperpycnal flows that entrained carcasses of trilobites and other organisms. In many cases, both Type I and II obrution was followed by additional sedimentation, geochemical zones moved upward through the sediment column, and there was little tendency to form diagenetic overprints. Alternatively, if burial was followed by an interval of sediment starvation, the sediments were bioturbated and very early diagenetic mineralization was superimposed, first, in rare cases, as mineralized soft parts in entombed carcasses, and later as pyritization of burrow linings. Development of the concretionary layers required more prolonged periods of stability of the sulfate reduction zone. Cementation of sediment shielded organism bodies from most or all effects of compaction. Thus, ironically, the best preservation of delicate remains required rapid burial, associated with mass mortality, and very low rates of background sedimentation following the event.

Comparative palynofacies, magnetic susceptibility and cyclicity of the Middle Devonian Müllertchen Section (Eifel area, Germany)

The recognition of subtle small-scale cycles in “monotonous” calcareous mudstone intervals requires a multi-disciplinary approach. In the classical Eifel area of Germany, a section of lower Givetian calcareous rocks is exposed in the well-known Müllertchen Quarry near Üxheim-Ahütte. Lying on top of limestones of the Lahr Member of the Ahbach Formation, a succession of calcareous mudstones (marlstones) is developed. This succession contains diverse brachiopods, corals and bryozoans, which are mostly small, especially in the lower part. In the present study, we focus on the combination of lithology, palynological content and magnetic susceptibility in order to evaluate whether a cyclic pattern is developed and can be mirrored by these methods. The lithological succession shows a rather homogenous marly sequence interrupted by a few more rigid calcareous beds; two of them are known as the Lower and Upper Wurmweide beds, which yield traces of Chondrites on the upper surface. For palynological analyses, 19 samples were obtained from a 4-m interval in the marly succession. Eighty samples were collected at regular spacing through the same interval, for magnetic susceptibility analysis. Palynofacies analysis has been carried out, and the assemblage of leiosphaerids, acritarchs, scolecodonts and miospores reflects the lithology. In particular, the distribution pattern, abundance and ratios of leiosphaerids and miospores can be applied for palaeoenvironmental interpretation. Patterns of change in proportion of these two groups match that of the magnetic susceptibility. These combined data indicate small-scale cyclicity, even within a relatively monotonous, thin stratigraphic interval.

Late Silurian and Devonian ostracods of the Istanbul Zone (Western Pontides) and the Taurides: palaeogeographical implications

Non-metamorphic Palaeozoic sedimentary successions without major breaks exist in the Istanbul Zone of the Western Pontides (northern Turkey) and in the Taurides (southern Turkey). Based on different proxies, a Gondwanan affinity has been determined for the Taurides; however, the palaeogeographical position of the Istanbul Zone is still controversial. The aim of this paper is to discuss possible contributions of late Silurian and Devonian ostracods to the palaeogeographical assignment of the Western Pontides (Istanbul Zone). Furthermore, ostracods of the Taurides have also been evaluated in terms of the palaeogeographical setting of this terrane. Late Silurian ostracods of the Istanbul Zone (Western Pontides) show close similarities at the species level with the assemblage from the upper Silurian (Ludlow) rocks of Baltica. This Laurussian affinity indicates a palaeogeographical setting to the north of the Rheic Ocean for the Pontides during the late Silurian. The Devonian ostracod assemblages of both the Taurides and the Istanbul Zone have an affinity to both Laurussia and Gondwana. Therefore, a faunal link should exist during this long period between Laurussia and Gondwana. The faunal link between the two palaeocontinents can be explained on the one hand by a narrow ocean with shallow pathways. On the other hand, a wider ocean with long-shore currents, with broad and shallow shelf areas and/or islands functioning as stepping stones would also allow a faunal link for benthic ostracods.