Odd palynomorphs (NPPs) from annuli of fern sporangia; Holocene lacustrine and tsunami deposits of the Danish Wadden Sea

Abstract

Odd palynomorphs are identified in sediments in a shallow core from the Rømø barrier island in the Danish Wadden Sea. The palynomorphs occur in five stratigraphic samples of lacustrine mud, peat and sand. The sand has a chaotic structure and was deposited by a tsunami associated with the Storegga slide in the North Atlantic Ocean, 8150 years ago. The palynomorphs are very common in the lower samples from in situ gyttja and peat and are less common in the overlying sand bed. Reworked lumps of peat occur in the sand and the palynomorphs are therefore also considered reworked into the sand during the tsunami event. The variable morphology of the palynomorphs is considered to represent the ontogeny as well as the specific morphology of fern annuli. The wall tissue of the sporangium is coherent with annulus cells and reveals the fern relationship. The tissue shows a characteristic succession of elongated, rectangular cells in the sporangium wall with stomium and annulus. The palynomorphs are interpreted as parts of annuli from sporangia of leptosporangiate ferns. The modern fern species Hemionitis glabella has a comparable sporangium morphology, and the palynomorphs are considered to come from a fern relative. Hemionitis is cosmopolitan but absent in Europe north of France. This annulus type and the derived palynomorph types have not been described from fossil material before.

Keywords:

• fern sporangium
• annulus
• palynomorph
• NPP
• Holocene

Acknowledgements

I extend my thanks to Prof. Dr Finn Surlyk and Dr Sofie Lindström for their invaluable support, advice and constructive criticism during the course of this study. Dr L. Shumilovskikh and an anonymous reviewer are thanked for their suggestions and comments. Annette Ryge prepared the samples and Jette Halskov edited and redrew Figure 1 from Fruergaard et al. (2015). The paper is published with the permission of the Geological Survey of Denmark and Greenland.

Disclosure statement

The author reported no potential conflict of interest.

Additional information

Funding

This study was funded by Geocenter Denmark Grant No. 603-00003.

Notes on contributors

Stefan Piasecki

Stefan Piasecki is emeritus at the GLOBE Institute, University of Copenhagen. His research focuses on palynology, stratigraphy and geology, especially on Permian–Triassic, Jurassic–Cretaceous and Neogene sediments based on fieldwork in Denmark and Greenland.