11. QUATERNARY DINOFLAGELLATE CYSTS FROM HOLE 552A, ROCKALL PLATEAU, DEEP SEA DRILLING PROJECT LEG 811

Detailed dinoflagellate cyst analysis of the Quaternary sediments recovered from Hole 552A, on the Rockall Pla-teau, by hydraulic piston corer (HPC), especially from Cores 1 and 2, has revealed three major "events " in the dinofla-gellate record. The oldest "event " separates a younger dinoflagellate-rich unit from the remainder of the older Quater-nary sequence, which for the most part either is entirely barren or contains only poor dinoflagellate floras. The second "event " marks the change at the top of the rich dinoflagellate unit to samples above that are again barren of cysts. The rich and diverse dinoflagellate assemblages recovered from the unit delimited by these two "events " are characterized in general by the species Opβrculodinium centrocarpum (Deflandre and Cookson) Wall, but with certain horizons domi-nated by Spiniferites spp. and Nematosphaeropsis labyrinthea (Ostenfeld) Reid. This unit is thought to be the dinofla-gellate cyst record of an interglacial environment at this latitude. The youngest "event " marks, in samples containing increasingly richer dinoflagellate assemblages, a significant change from a Bitectatodinium tepikiense Wilson domi-nated assemblage to one dominated by O. centrocarpum, as the climatic/environmental conditions ameliorated into the Flandrian. It is thought that this youngest "event " in the dinoflagellate record can be correlated from the Goban Spur area (DSDP Leg 80) through Rockall and possibly into the North and Norwegian seas. Unfortunately samples from the Quaternary sediments in the remaining holes (i.e., Holes 553B, 554, and 555) contained such poor floras as to preclude useful discussion.