Rich palynomorph assemblages occur throughout the Campanian to Eocene stratigraphic section of Seymour and surrounding islands, northeastern Antarctic Peninsula. The section comprises sediments referred to the López de Bertodano, Sobral, Cross Valley, and La Meseta Formations. Nearshore marine to coastal-deltaic sediments include marine palynomorphs (dinoflagellate cysts, acritarchs, other algae) and diverse land-derived palynomorphs (pollen, spores, fungal spores, fresh-water algae), plus a variety of other organic debris. Palynostratigraphic results are based on a survey of about 530 outcrop samples of Campanian through Paleocene age. Six palynomorph zones, informally designated 1 through 6 and based on dinocyst species, are recognized in the upper Campanian through Paleocene section on Seymour Island. López de Bertodano sediments include zones 1 to 4 of late Campanian to Maastrichtian age. These Cretaceous zones are characterized by an evolving complex of dinocyst species of Manumiella and related genera. Zone 5, of early Paleocene age, occurs in uppermost López de Bertodano Formation sediments and most of the Sobral Formation on Seymour Island. Zone 6, of probable late Paleocene age, occurs in the uppermost Sobral Formation. Paleocene zones 5 and 6 are characterized by dinocysts Spinidinium spp., Deflandrea and Ceratiopsis spp., Microdinium sp.; and Paleoperidinium pyrophorum in zone 5. Two distinct older assemblages of middle to late Campanian age are recognized from The Naze, situated on northeastern James Ross Island, and Cape Lamb, on Vega Island. Upper Cretaceous-Paleocene nonmarine palynomorphs reflect a cool, humid, podocarpaceous conifer vegetation with a varied understory of ferns and highly endemic angiosperms.

Unconsolidated, fine-grained (sandy silts), shallow marine sediments of the upper Lopez de Bertodano Formation include the Cretaceous/Tertiary boundary on Seymour Island, northeastern Antarctic Peninsula. These strata contain abundant palynomorphs and other micro- and macrofossils. The Cretaceous/Tertiary boundary is provisionally placed at a dinocyst zonal boundary that occurs within a laterally persistent glauconite-rich interval. This glauconite interval marks the highest, definitely in-place Maastrichtian macro- and microfossils. Strata above this interval are considered Danian, based on palynological evidence, in the absence of other age-diagnostic fossils. Association of Maastrichtian ammonites and microfossils with typically “Danian” dinocysts below the glauconite interval accentuates the transitional nature of the Cretaceous/Tertiary succession on Seymour Island. Changes in Cretaceous/Tertiary dinocyst assemblages may be related to local environmental change, including regression. Pollen and spore assemblages record little change and no evidence of an abrupt event for the land vegetation across the Cretaceous/Tertiary boundary. Instead, a longterm floral turnover is inferred from nonmarine species. This gradual change is consistent with climatic change, possibly cooling, through much of Maastrichtian and early Paleocene time.