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

Abstract

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.