High-resolution dinoflagellate cyst biostratigraphy of the Santonian-basalCampanian (Upper Cretaceous): new data from Whitecliff, Isle of Wight, England

Results are presented of a high-resolution study of dinoflagellate cysts fr om part of the Upper Chalk succession on the Isle of Wight, southern Englan d. The section was logged in detail, and stage and zonal boundaries were lo cated using macrofossil data. Lower and middle Santonian samples are domina ted by species of Senoniasphaera, Canningia, Circulodinium and Heterosphaer idium. Major changes in the dinocyst assemblages coincide with the base of the upper Santonian Uintacrinus socialis crinoid Zone, with an increase in abundance and diversity, and a shift to assemblages dominated by Spiniferit es spp. and Palaeohystrichophora infusorioides Deflandre. Our palynological records (114 dinocyst, 4 acritarch species) provide the basis for a new ev ent stratigraphy. Cyclonephelium filoreticulatum (Slimani) Prince, Jarvis e t Tocher, comb. nov. temporarily disappears and an acme of Heterosphaeridiu m? heteracanthum (Deflandre et Cookson) Eisenack et Kjellstrom occur in the lower Santonian. The total range of Renidinium rigidum Prince, Jarvis et T ocher, sp. nov. and the FAD of Senoniasphaera protrusa Clarke et Verdier em end. lie within the middle Santonian. Raetiaedinium truncigerum (Deflandre) Kirsch and Pervosphaeridium monasteriense Yun first appear, and Hystrichos trogylon membraniphorum Agelopoulos reappears around the base of the upper Santonian. The FADs of Pervosphaeridium intervelum Kirsch and Thalassiphora ? spinosa (Clarke et Verdier) Foucher, and the reappearance datums (RADs) o f Chlamydophorella nyei Cookson et Eisenack, Subtilisphaera pontis-mariae ( Deflandre) Lentin et Williams and Membranilarnacia polycladiata Cookson et Eisenack occur in the upper Santonian. No major changes in dinocyst assembl ages occur at the Santonian/Campanian boundary, but a sequence of LADs occu r in the basal lower Campanian, in the order: Xenascus perforatus (Vozzhenn ikova) Yun; Spinidinium echinoideum (Cookson et Eisenack) Lentin et William s; Surculosphaeridium? longifurcatum (Firtion), Davey et al.; Raetiaedinium truncigerum (Deflandre) Kirsch and S. protrusa; Florentinia ferox (Defland re) Duxbury; Acanthaulax wilsonii Yun and T.? spinosa, The range of Endoscr inium campanula (Gocht) Vozzhennikova extends into the upper Santonian. Add itional taxonomic proposals are: Senoniasphaera Clarke emend.; S rotundata Clarke et Verdier emend,; Circulodinium latoaculeus (Yun) Prince, Jarvis et Tocher, comb, nov. (C) 1999 Elsevier Science B.V. All rights reserved.