Early Pleistocene pollen biostratigraphy in the central North Sea

Abstract

Three Early Pleistocene profiles from BGS boreholes 81/29, 81/34 (Devil's Hole area) and 81/26 (Fladen Ground) are correlated with each other on the basis of pollen biostratigraphy and with reference to pre-existing palaeomagnetic data. The profiles are also correlated with the pollen-based Dutch composite stratigraphy for which a good correlation with the geomagnetic polarity time scale exists. Comparisons are drawn between existing palaeoenvironmental reconstructions from marine microfossil data from the profiles and from the Dutch pollen stratigraphy. The Devil's Hole boreholes are interpreted as younger than the Olduvai geomagnetic event as massulae of the freshwater fern Azolla filiculoides, a species that did not appear before that event, is present in a reversed polarity sequence. Considerable freshwater influx at the base of all three pollen profiles can probably be related to delta progradation from the south during Early Pleistocene times. In the Devil's Hole sequences, elevated frequencies of pre-Quaternary spores are also registered in the upper part of this freshwater-influenced interval, indicating the persistence of onshore erosional activity, probably glaciation. This interval is interpreted as of Menapian age, a stage during which increased delta progradation and the first Quaternary regional glaciation occurred in northwestern Europe. A hiatus in the Devil's Hole vicinity separates the Menapian interval from a sequence correlated with the latest part of the Bavel interglacial (Bv 5) i.e., in the upper part of the Jaramillo geomagnetic event. During the earlier phase of the succeeding Linge Glacial strong fluvial discharge at first influenced the Devil's Hole area after which calm arctic to high arctic marine conditions prevailed (as indicated by the marine microfossil data) in a depositional environment influenced by meltwater from the British ice sheet. The later part of the Linge glacial in the Devil's Hole area contains pollen spectra indicating glaciofluvial influences from the Scandinavian ice sheet and foraminiferal assemblages indicating ameliorated climatic conditions.