Taphonomy of neopterygian fishes from the Upper Kimmeridgian Wattendorf Plattenkalk of Southern Germany

Abstract

The Upper Kimmeridgian Wattendorf Plattenkalk, the oldest of the Solnhofen-type plattenkalks of southern Germany, has yielded a high number of exceptionally preserved fossils over the past several years. The high number of fossils and the fact that every bedding plane, along which the laminated rocks split, has been equally thoroughly searched for fossils, allow for qualitative as well as quantitative taphonomic investigations. For a quantitative analysis of the Wattendorf lagerstatte, four different taphofacies (A–D) were established by means of euclidean cluster analysis. For this, biostratinomic features of neopterygian fishes, primarily of the genus Tharsis, were recorded. Percentages of the occurrence of these features per layer were determined and clustered into groups of similar patterns. The taphonomic features utilised were bending of the spinal column, completeness, and skeletal articulation. Taphofacies A through D mark a change from a palaeoenvironment with only small extrinsic disturbing factors to a palaeoenvironment characterised by greater disturbance (e.g. bottom currents, fluctuating salinity). At the beginning of plattenkalk deposition, cyclic changes of the palaeoenvironment prevailed with periodic high disturbance, probably caused by storm-induced flows. These events initiated mixing of the supposedly chemically stratified water body. In the upper part of the plattenkalk unit, taphofacies indicative of higher disturbance dominate, suggesting a change from stable to less stable environmental conditions in the plattenkalk basin resulting in disruption of the typical plattenkalk sedimentation. Sporadic oxygenation of bottom waters is also indicated by the style of soft-tissue preservation. Besides typical phosphatisation, a specimen of Palaeohirudo? sp. shows soft-tissue preservation through iron-oxide permineralisation.