Late Pleistocene floras from Earith, Huntingdonshire.

A pit in fluviatile gravel of the River Ouse at the western edge of the East Anglian fenland has exposed several richly organic beds of Last-glacial age. A radiocarbon date of 42 000 years from one bed confirms the terrace stratigraphy in placing the beds in a fairly early part of the Weichselian. The organic beds are succeeded by cryoturbation phenomena and ice wedge casts, indicating a severely cold climate with permafrost. The beds represent former pools on the flood-plain into which plant detritus was washed from the surroundings, chiefly by melt water in the spring. Pollen is sparse, but the macroscopic plant remains indicate a vegetation dominated by dwarf willows, accompanied by many herbs of base-rich, open habitats. Identification of the macrofossils is discussed and comments are made on the ecology and taxonomy of important species. The flora contains a mixture of northern and southern distributional types, the southern including species requiring a July mean temperature approaching 16 °C. Halophytes are frequent, and four species are considered to be obligate halophytes and to demonstrate the presence of salt in the substrate. The plant mixtures are explained as a result of the peculiarly open habitats of the glacial landscape and of the climate, which appears to have had warm summers and very cold winters, with a mean annual temperature slightly below 0 °C, resulting in discontinuous permafrost.