Taphonomy of dense ophiuroid accumulations from the Middle Triassic of Poland






Michał Zatoń[mzaton@wnoz.us.edu.pl], Mariusz A. Salamon [paleo.crinoids@poczta.fm], Andrzej Boczarowski [boczar@us.edu.pl] and Sławomir Sitek [sitek1@wp.pl], Faculty of Earth Sciences, Będzińska 60, PL–41-200 Sosnowiec, Poland; manuscript received on 08/07/2005, manuscript accepted on 02/07/2007.


The taphonomy of three Middle Triassic (Muschelkalk) monospecific ophiuroid taphocoenoses, comprising Aspiduriella similis (Eck), from different regions in Poland (Holy Cross Mountains, Upper Silesia and North-Sudetic Basin) has been investigated. The majority of specimens (88.5% of a total of 428 individuals) are partially disarticulated, having only proximal and median portions of their arms preserved (Taphonomic Group 2). Pristine specimens, with only faint traces of disarticulation (Taphonomic Group 1), as well as those that preserve the disc only, or which have only proximal stumps of arms preserved (Taphonomic Group 3), are much rarer (6.5% and 5%, respectively). Moreover, most specimens (76.4%) are oral side up. Only 19.2% of specimens are preserved in life position, and a small fraction (4.4%) are preserved oblique to bedding. All ophiuroids studied occur in thin, pelitic layers devoid of any trace fossils. Associated body fossils, such as bivalves, gastropods or crinoids, are very rare. Taking into account ophiuroid taphonomy, as well as sedimentological characteristics of the thin layer (burial layer), it is clear that all assemblages were transported prior to burial. The predominance of articulated skeletons indicates that the burial event (obrution event) was not only rapid, but also single – subsequent events would have destroyed the previously buried ophiuroids. Storm-related resuspension of fine-grained material from nearshore environments which covered the ophiuroids is the most likely burial agent. The fact that in all regions the ophiuroid taphofacies studied is identical suggests that the three assemblages underwent the same burial history, and that a single event might have been responsible. inline image Muschelkalk, ophiuroids, Poland, taphonomy, Triassic.