Palynostratigraphy of dinosaur footprint-bearing deposits from the Triassic–Jurassic boundary interval of Sweden

Abstract

The Triassic–Jurassic boundary (c. 200 Ma) marks one of the five largest Phanerozoic mass extinction events and is characterized by a major turnover in biotas. A palynological study of sedimentary rock slabs bearing dinosaur footprints from Rhaeto–Hettangian strata of Skåne, Sweden was carried out. The theropod dinosaur footprints (Kayentapus soltykovensis) derive from the southern part of the abandoned Vallåkra quarry (Höganäs Formation) and were originally dated as earliest Jurassic (Hettangian) based on lithostratigraphy. Our results reveal that two of the footprints are correlative with the latest Triassic (latest Rhaetian) disaster zone typified by a high abundance of the enigmatic gymnosperm pollen Ricciisporites tuberculatus and Perinopollenites elatoides together with the key taxon Limbosporites lundbladii and fern spores. Two footprints are dated to correlate with the Transitional Spore-spike Interval. One footprint is interpreted as Hettangian in age based on the relatively high abundance of Pinuspollenites spp. together with the presence of the key taxa Retitriletes semimuris and Zebrasporites intercriptus. Our new palynological study suggests that the Kayentapus ichnogenus already appeared in the end of Triassic, and our study highlights the use of palynology as a powerful tool to date historical collections of fossils in museums, universities and elsewhere. The Hettangian footprint reflects a marine influence while all other studied ichnofossil specimens occur in non-marine (floodplain and delta interdistributary) sediments. The sediments associated with the Hettangian footprint include a significant proportion of charcoal transported from land after wildfires. The Rhaeto–Hettangian vegetation was otherwise characterized by multi-storey gymnosperm–pteridophyte communities.

Keywords:

• Triassic–Jurassic
• dinosaur footprints
• ecological crisis
• palynology
• Sweden

Acknowledgements

The authors thank Drs G. Niedźwiedzki and S. Poropat for their valuable review with extensive feedback which unquestionably improved our paper. The authors would like to thank an anonymous reviewer for comments on the palynology. This research was supported by the Swedish Research Council under Grant LUCCI (Lund University Carbon Cycle Centre) to V. Vajda and Grant 621–2011–4922 to M. Calner. V. Vajda is a Royal Swedish Academy of Sciences Research Fellow funded through the Knut and Alice Wallenberg Foundation. Andrea Santivanez is thanked for taking the pollen micrographs and Russ Harms GeoLab Ltd for palynological processing.