Exceptional preservation of Late Jurassic trace fossils in a modern cave (Mühlbachquellhöhle, S Germany)
Wisshak, Max; Jantschke, Herbert
published: Jul 11, 2008
ArtNo. ESP155024901005, Price: 29.00 €
From the unusual outcrop of an active river cave (Mühlbachquellhöhle, S Germany), well-preserved Late Jurassic (Kimmeridgian) trace fossils, produced by soft-bottom dwelling organisms in an epicontinental sea, are reported. Three types of vertical burrows are exposed by corrosion on the cave's ceiling and walls: less than 1 mm thick, rarely branching tubular structures (ichnogenus Trichichnus), 3-5 mm thick vertical traces (Skolithos) with rare horizontal protrusions or Y-shaped branching (Polykladichnus), and 10-20 mm thick irregular vertical structures with affinities to Skolithos. They exhibit a range of preservational styles, comprising combinations of voids and sediment-, spar-, or pyrite infills. The trace fossil genesis is interpreted as deep burrowing, reaching down to reducing levels in the seafloor, with the presence of an organic lining preventing collapse and catalysing the development of a pyrite infill. Remaining voids were partly filled with calcite spar, possibly during early burial diagenesis in the zone of anaerobic methanogenesis by the re-precipitation of dissolved aragonite. Subsequent stages of differential burial diagenesis led to the development of the limestone-marlstone alternation with a compaction of the trace fossils only in the marlstone layers. The potential of caves as natural outcrops, where well-preserved fossils and trace fossils can be studied in situ is emphasised, and the obligation of a non-destructive approach is pointed out.