PALYNOLOGY OF ORGANIC BEDS BELOW DEVENSIAN GLACIGENIC SEDIMENTS AT PEN-Y-BRYN, GWYNEDD, NORTH WALES

Pollen diagrams from organic facies overlain by glacigenic sediments a t Pen-y-bryn, North Wales (53 degrees 7'N, 4 degrees 16'W), suggest th at it is the first locality in the British Isles to provide evidence f or several Devensian interstadials prior to Devensian stadial glaciati on(s). The evidence is not, however, unequivocal. At least two main ep isodes of organic sedimentation are indicated, separated by an interva l of uncertain duration. One eposide records a Pinus-Picea-Betula fore st. A second, possibly later, event, with tree pollen less than 10% of total land pollen (TLP), suggests a cool, largely unforested environm ent. A third episode, with tree pollen up to 25% of TLP, may be relate d to the latter or be of intermediate age, whereas a fourth and later episode of organic accumulation may be of reworked material. Radiocarb on dating of organic deposits and of a wood macrofossil enclosed in ba sal till is inconclusive, as is preliminary uranium-series dating. The principal biogenic episodes may correlate with Oxygen isotope Substag es 5c and 5a, but as the pollen records reflect facies floras, the cor relation remains tentative; it is also possible that other temperate p eriods are recorded. Further resolution of the chronostratigraphy is r equired to help clarify the problematic correlation of interstadial an d stadial events in northwest Europe and to correlate more accurately the biogenic and glacigenic facies at Pen-y-bryn with their Pleistocen e equivalents elsewhere.