The Devensian periglacial record on Thanet, Kent, is traced from c. 88 to 74 ka and from c. 24 to 12 ka by optical luminescence dating of aeolian sand and silt in the periglacial stratigraphy. The record commences before 88 ka with valley cutting at Pegwell Bay. Valley filling had begun by c. 88 ka and continued to at least 74 ka, coinciding with a major episode of loess deposition in Europe. Permafrost aggradation commenced before c. 21 ka, brecciating near-surface chalk by ice segregation in permafrost and the overlying active layer. Deposition of aeolian sand (coversand) occurred at c. 24 21 ka, correlating with the Older Coversand I in mainland Europe. Permafrost degradation commenced at c. 21 ka, probably due to climate warming during Greenland Interstadial 2. The resulting active-layer deepening through ice-rich permafrost initiated soft-sediment deformation and formation of large-scale patterned ground in an active layer c. 2m deep. Renewed permafrost aggradation between c. 21.25 and 18 ka coincided with climate cooling during Greenland Stadial 2c and led to cryoturbation in a thinner active layer. Final permafrost degradation commenced no later than c. 14.7 ka, that is, the start of Greenland Interstadial 1e, and may have occurred to some extent during the climate warming associated with Greenland Stadial 2b (c. 19.5 16.9 ka). Renewed deposition of aeolian sand took place at c. 15.5 ka, coincident with loess deposition on Thanet. A final episode of aeolian sand deposition occurred at 12 ka, correlating with the Younger Coversand deposits that are widespread in northwest Europe and formed during Greenland Stadial 1

Changes in morphological variability within fossil populations of planktonic protists provide insight into the processes responsible for morphological change. Evolution in the radiolarian genera Theocorythium and Lamprocyclas is documented biometrically in Pliocene and Pleistocene core material from the equatorial Pacific and Indian Oceans. The patterns of morphological change in Theocorythium within a single Pacific core could be interpreted as indicating the in situ evolution of T. trachelium trachelium from T. vetulum via intermediate forms during the Pleistocene. However, consideration of biogeographic data shows that this is not the case and supports instead two alternate interpretations: (1) immigration coupled with extensive hybridization and introgression, or (2) multiple polymorphs of a single species changing in frequency along a cline. Analyses of evolutionary change in Theocorythium and the closely related genus Lamprocyclas during the Pliocene suggest that hybridization may be a significant factor in the production of new species. Evolutionary models and phylogenetic analyses should consider that barriers to gene flow may vary significantly with time and permit the exchange of genetic information between populations previously reproductively isolated.

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