Palaeozoic, Mesozoic and contemporaneous megaspores from the Tertiary of southern England: indicators of sedimentary provenance and ancient vegetation

Abstract

Megaspores are recorded from several localities in the Thanet and Reading Beds (upper Palaeocene) of southern England. Evidence from their taxonomic affinity, colour, compression and state of preservation indicates three separate groups: two reworked from lower Westphalian Coal Measures and Lower Cretaceous sequences, respectively, and one of contemporaneous forms. Mesozoic megaspores redeposited in the British Tertiary have not previously been recorded. Isolated Carboniferous forms have been found before but their possible value in provenance studies has not been fully explored. The new material includes a diverse assemblage of numerous Westphalian and Lower Cretaceous forms from a single horizon in the Thanet Beds. Of possible source areas it seems most likely that these spores were reworked from the Moray Firth Basin, and elsewhere near the present eastern coast of Scotland, by means of longshore drift following a roughly N–S palaeocoastline. Evidence from other studies of heavy mineral assemblages and palaeogeography also indicates derivation of Thanet Beds sediments by this means. The Cenozoic megaspores include an Azolla (water fern) and two distinct lycopsid forms, one probably of selaginellalean and one of isoetalean affinity. These latter provide the first clear evidence of lycopsids in British Tertiary floras and expand our knowledge of freshwater macrophytes of that time. The assemblages of Minerisporites show morphological trends which may prove to be of biostratigraphic value.