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

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.