Diverse and abundant organic walled microplankton have been recovered from the only known outcrops of lower Tertiary marine sediments in the Antarctic area. The 70 samples collected from the Paleogene Seymour Island deltaic complex yielded 43 genera and 74 species of dinoflagellate cysts; 2 genera and 9 species are new, and a number of new combinations and taxonomic emendations are proposed. Specimens attributable to the Acritarcha, Pterospermatales, and Chlorococcales also were noted. Sediments of the Cross Valley Formation in the Cape Wiman area are early late Paleocene in age. The exact source of samples reputedly collected from the Cross Valley Formation at the type locality in Cross Valley is uncertain. This is because faults and surface slumps in the area were only partially mapped at the time of sampling. The lower 100 m of Section 12-13 are Eocene in age, whereas the overlying 20 m are no younger than early late Paleocene. The deposits of the stratigraphically higher La Meseta Formation can be subdivided into beds of late early and middle to late Eocene age. Deposition occurred within the subenvironments of the Seymour Island Paleocene-Eocene deltaic complex. Specific paleoenvironments identified include distributary channels, interdistributary bays, lagoons, and perhaps, prodelta areas. The Paleocene dinoflagellate cyst floras are composed of cosmopolitan taxa. Eocene floras include cosmopolitan and provincial taxa. The cosmopolitan taxa have been reported from regions as widely separated as Europe, North America, and Australia. The provincial taxa belong to the hypothesized transantarctic flora that was well developed in and around Antarctica during the Eocene. The distribution of the transantarctic flora suggests that a marine seaway across West Antarctic connected the southwest Atlantic and southwest Pacific oceans during Eocene time. Rare, extra-Antarctic occurrences of some species included in the transantarctic flora suggest that such species should not be considered part of this flora, that the distribution of these taxa was bipolar, or that the complete distribution of the transantarctic flora is yet to be documented.

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.

The Cretaceous-Paleogene sequence on Seymour Island has been mapped in terms of four previously named units: the López de Bertodano Formation (Cretaceous-Paleocene), the Sobral Formation (Paleocene), the Cross Valley Formation (late Paleocene), and the La Meseta Formation (Eocene). The basal surfaces of the Sobral and Cross Valley Formations include portions with clear evidence of erosional unconformity. The base of the La Meseta Formation laps onto a steep buttress unconformity at both of its exposed margins. The scale of lenticularity of the units increases upward throughout the sequence. The López de Bertodano Formation and most of the Sobral Formation are built of essentially tabular units, and have been effectively characterized by isolated measured sections. The Cross Valley Formation is a channel-filling lens. The La Meseta Formation has a complex, asymmetric, trough-like form. It is built of large-scale lenses characterized by different shelly facies that do not all extend across the full width of the trough. Consequently, mapping between measured sections is essential to establish the lateral relationships. Even then, the geometric relationships do not identify time lines; establishing the real age relationships will require very carefully located faunas. The observed relationships between the length and height of lenticular units can be used to estimate the expected vertical error when faunas are projected into a composite section. The whole sequence is essentially a gently dipping homocline. The youngest units have slightly gentler dips, indicating progressive or repeated tilting. But a larger component of the variance in bedding attitude is contributed by steeper dips in the sedimentary filling of channels and slump scars. The regional tilt, the development of growth faults, facies changes, and the orientation of erosional surfaces have a symmetrical arrangement from which a common cause is inferred. The best estimates of the timing of the major unconformities and erosional episodes are only partially compatible with current models of global sea-level change.

Numerous carbon films and leaf impressions have been recovered from a Paleocene locality of the Cross Valley Member of the Sobral Formation and from two horizons of the middle to late Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula. These fossil megafloral assemblages are dominated by specimens of the genus Nothofagus, the Southern Beech, with representatives of araucarian and podocarp conifers and several species of ferns. The fossil material of Nothofagus exhibits a strong similarity to species of that genus from southern South America and indicates that the paleoclimate of the Antarctic Peninsula was cool temperate during the early Tertiary. The association of this plant material with fossil marsupials of the family Polydolopidae and the dependence of Nothofagus on overland seed dispersal strengthen the contention that the hypothesized Weddellian Province reconstruction of Gondwanaland during late Cretaceous and early Tertiary time was a continuous coastal, cool, temperate biogeographical province.