An enigmatic trace fossil from the Upper Triassic (Rhaetian) shales of Western Europe

Abstract

Various trace fossils are known from the Upper Triassic (Rhaetian) shale deposits of western Europe, especially from Great Britain. Here we present a unique specimen, unknown from Rhaetian shales in western Europe thus far to our knowledge. The specimen consists of a string of small knobs collected from the dark-coloured Rhaetian shales from the eastern Netherlands, deposited in a marine, near-coastal environment. The specimen represents the first described trace fossil from these shales. The identity of this specimen appears enigmatic. However, SEM-EDS analysis showed that the string of knobs is pyritised and does not contain phosphorus nor did the sediment directly around the specimen, suggesting a non-coprolitic origin of the specimen. Eggs and larvae are also excluded as possibilities. The specimen closely resembles several trace fossils identified as burrows, which is why we favour this interpretation. The rare presence of trace fossils reinforces the hypothesis that the Dutch Rhaetian shales were deposited under a stresses regime with low oxygen conditions.