News from Schallodenbach

The tuff no.2 of the Donnersberg formation contains hard fossiliferous cherts which can be found on fields near Schallodenbach. Apparently there is not much diversity in the fossil content, which is mainly restricted to Gymnosperm rootlets, microbial layers, wood fragments and ostracod shells. The specimen shown here is one of the rare pieces with well preserved other plant parts which deserve closer inspection.

It is a fist-size specimen with light-coloured matrix without visible lamination (Fig.1). There are many healed cracks in the chert, some of them filled with white agate. Colour and degree of silicification vary on the surface of the layer. The cut face reveals black gymnospermous wood fragments of Dadoxylon type, as indicated by the presence of narrow pith rays, only one cell wide. An exact identification will require additional cuts and investigations. The more or less rounded edges may be due to wear in transport or to burning. Scattered between the wood morsels there are delicate remains of what seems to be twigs and leaves. The opaque matrix precludes a 3D-aspect but detailed anatomical observations can be made on the cut faces.

Fig.1: chert with plant debris

Fig.2 shows a small twig fragment with leaves in slightly inclined longitudinal section. The twig is seen to be subdivided into four segments with rather long leaves on the nodes. The small cross-sections seen in the vicinity are probably also leaves belonging to this twig. Quite interesting is their shape near the axis. The lower side is slightly concave, covering a kind of cavity between the nodes, possibly the site where sporangia had been. There is some similarity with Metacalamostachys dumasii strobili from Chemnitz-Altendorf. This would be compatible with the presence of Calamites gigas compressions in the Donnersberg formation if the leaves were not much longer than the bracts on the cones from Saxony. As a different explanation, the object could be the basal part of a strobilus or the branch immediately below the strobilus, as suggested by the absence of sporangia.

Fig.2: strobilus or branch with long leaves

Elsewhere on the sample face another branch with leaves is seen in tilted cut. Apparently the cut plane crosses a node, judging from a leaf base shaped as a small hump on the axis. In Fig.3 the conducting strand of this leaf is seen near that of the axis. The structure of the leaf is seen in some detail: A thin epidermis of one cell layer covers parenchymatic tissue of about 0.2 mm thickness which is subdivided into palisade parenchyma, the site of photosynthesis, and spongy parenchyma serving as transpiratory tissue on the lower side of the leaf. The two types of parenchyma are distinctly seen (Fig.4), except near the axis.

		Fig.3: tilted section of a branch with leaves
		Fig.4: leaves with parenchyma of palisade and sponge types

This sample contains more plant fragments with well preserved tissue. The structures shown here are to be thoroughly investigated after further cutting, also with the aim to find stomata. We hope that the analysis of sections will provide enough information for reconstructions of plant organs.

text & photographs: R. KRETZSCHMAR/Chemnitz