Approximately 150 meters of fine-grained Campanian sediments and over 100 meters of fine- to medium-grained Eocene sands underlie Pliocene basalts and conglomerates on Cockburn Island, northeastern Antarctic Peninsula. The Campanian beds are part of the "Unnamed strata" of the Marambio Group and contain invertebrate and palynomorph fossils that predate the adjacent Seymour Island López de Bertodano succession. Rich palynomorph floras suggest a middle Campanian Age. Deposition was in low energy, shallow shelf environments. Invertebrate and palynomorph fossils, and lithology, all indicate correlation of the Eocene beds with the basal La Meseta Formation, members Telm 1 and lower Telm 2 of Seymour Island. The age of these beds is probably late early Eocene. The basal La meseta sands are marginal marine to shallow shelf sediments that fill a broad valley probably incised during latest Paleocene-earliest Eocene as a result of tectonism and sea-level lowstands.