Megaspore assemblages from the Jurassic and lowermost Cretaceous of Bornholm, Denmark

Abstract

There are more than 600 slides containing megaspores in "Helge Gry's collection", housed at the Geological Survey of Denmark in Copenhagen. The majority of the specimens are unnamed, all are from the Danish island of Bornholm in the Baltic Sea, and none has been described hitherto. The stratigraphic distribution of 22 of the taxa was, however, taken into account in a paper by Gry, published in 1969, and 16 of these were illustrated by small line drawings. He considered the lithology, areal extent and depositional history of what were thought at the time to be only Jurassic strata on Bornholm. The youngest part of the succession he discussed, the "Purbeck beds" (Rabekke and Robbedale Formations), are, however, now known to be mainly, if not entirely, of earliest Cretaceous age. In the present paper Gry's megaspore records are brought up to date so that they can be used more effectively along with other microfossils in drawing biostratigraphical and palaeoenvironmental conclusions. All 22 taxa to which he referred are discussed and illustrated, mostly with scanning electron micrographs, and their nomenclature emended where necessary. Descriptions and figures of an additional 15 forms encountered in the collection are included. Three of these arc new species of megaspores and one is a palynomorph of uncertain origin, named Henrisporites bornholmensis, Paxillitriletes kristinae, P. rasmusii and Aneuletes discus respectively. Most, if not all, of the megaspores in Gry's collection are likely to have selagincllalean or isoetalcan affinities. There is no evidence of the presence of heterosporous water ferns. The assemblages differ significantly in composition according to their relative ages, with several forms being of considerable biostratigraphic value. There is, however, still room for greater precision in determining local stratigraphic ranges, and also a need to apply occurrence data to palaeoenvironmental interpretations. This will require carefully documented collecting of new samples.