The taphonomy of the Anisian of Winterswijk - insights into a unique environment

Abstract | The Triassic rocks of the Winterswijkse Steengroeve offer a unique window into the history of our planet. Preserved are mainly the remains of Sauropterygia, fi sh and invertebrates in various grades of completeness. The environment of these marine animals such as Nothosaurus was a special place where life was able to thrive despite diffi cult circumstances. Their skeletons can provide valuable information that can be unraveled through taphonomy, literally the laws of the grave. We notice, when looking through the many private and public collections, that the Winterswijk fossils show very diverse patterns ranging from isolated bones to almost complete skeletons. But what causes these variations, and what does this mean for the interpretation of the depositional environment? Here, we will discuss these patterns and support the existing taphonomical analysis by adding sedimentological evidence. This research on the skeletons from Winterswijk shows that the animals lived in shallow water and washed ashore on the carbonate mud fl ats after their death. There, the skeletons fell apart due to the water movements. The better-preserved skeletons must have been protected from these processes by natural depressions in the sediment, or were overgrown by the present microbial mats. Sedimentology, the structure of the rock itself, provides more evidence for this environment. Petrological thin sections confi rmed this interpretation of the depositional environment. The biolaminates, or ‘bindstones’ were capable of trapping vertebrate remains that were deposited by higher-energy events characterized by slightly coarser sediment. Furthermore, the larger grain size in layer 14 than in layer 9 shows an increase of energy in the environment.