Whale bones from the upper Eocene — ?lower Oligocene La Meseta Formation of Seymour (Marambio) Island, West Antarctica, are assigned to the Archaeoceti. They most probably belong to an undetermined genus of the family Basilosauridae Cope. 1867; subfamily Dorudontinae Barnes and Mitchel. 1978.
Fossil bird remains assignable to ratites (palaeognathous birds) are described from the Paleogene strata of the La Meseta Formation of Seymour Island, Antarctic Peninsula. This record sheds new light on Gondwana's avian history.
Mineral composition of bedrock is the main factor determining salt mineralization in the weathering zone of Seymour (Marambio) Island (maritime — Antarctic continent climatic boundary). Supply of salts by sea water spray can accelerate weathering process, modify chemical formula of salt minerals and give ephemeral efflorescences of easy soluble chlorides and partially longer lasting gypsum on the surface. Microbiologically mediated oxidation of sulphides and followed acid sulphate drainage formed K and Na jarosite, basic amorphous aluminium sulphate, gypsum, aluminium bearing ferrihydrite and ankerite in weathering zone of Paleogene sediments. Intense alteration of well-lithified, calcareous sandstones of unit 1 of the López de Bertodano Formation (Cretaceous) on old erosion surface led localy to surface mineralization comparable with that found in Antarctic Continent. Stones laying on the soil surface are covered by thin red film of ferrihydrite above the soil level and by light green crust of aragonite coloured by glauconite pigment on the underground side. Most of the Cretaceous sediment does not contain sulphides nor alteration susceptible silicates thus ephemeral sea salts efflorescences observed on its surface are more prominent than in another places.
Basing on isolated vertebrae, fossil fishes of the order Gadiformes have been first discovered in sediments of the La Meseta Formation (upper Eocene — ?lower Oligocene) on Seymour (Marambio) Island, West Antarctica. This is one of the oldest and the only locality with the Gadiformes skeletal remains in the Southern Hemisphere. Other poorly preserved centra have been determined as Teleostei (order incertae sedis).
Isolated and fragmented jaws, a single basioccipitale and vertebrae of the Gadiformes, indeterminate family and genus, are described from Eocene sediments of the La Meseta Formation, Seymour Island, Antarctic Peninsula. Based on the dentition and other characters of both jaws they are assigned an informal name of „Mesetaichthys". The remaining isolated bones belong probably to the same form.
This report describes aims and preliminary results of geological fieldwork carried out by a joint Argentine-Polish party on Seymour (Marambio) and Cockburn islands. Antarctic Peninsula, during austral summer of 1987 88. Seymour Island exposes chiefly shallow-marine, fossiliferous siliciclastic sediments that form an upper, 2000 m thick part in the Mesozoic-Tertiary backarc basin-infill of the Antarctic Peninsula. The fieldwork centered on paleontology and sedimentology of the La Meseta Formation (upper Eocene- ?lower Oligocene), although some observations of older deposits were carried out also. Clupeoid fishes were discovered in the La Meseta Formation. This is the first record of such fish fossils on the Antarctic continent.
A sequence of glacial deposits up to 4 m thick unconformably overlies the Eocene La Meseta Formation on the Seymour Island plateau (meseta) and forms a lithostratigraphically distinct unit in the succession of the James Ross Basin, which is formally named here as the Weddell Sea Formation. The formation is thus far known only from Seymour Island. This is a terrestrial melt-out till which contains abundant erratics and also reworked Cretaceous–Tertiary micro- and macrofossils within a silty clay matrix. The terrestrial origin of this till is shown by glacial striations at the base of the unit. The largest erratics (up to 3 m in diameter) are composed of plutonic (granitoids) and metamorphic (gneiss and crystalline schist) rocks of the Antarctic Peninsula provenance. Smaller in size and much more numerous are erratics of volcanic rocks, represented by andesite, basalt and corresponding pyroclastics of the James Ross Island Volcanic Group. Less common are erratics of sedimentary rocks, sometimes bearing fossils derived from the underlying Tertiary and Cretaceous strata. A few erratics from the top of the studied sequence are conglomerates of the Cockburn Island Formation with a foraminifer fauna. These are the youngest clasts within the Weddell Sea Formation. The presence of the Pliocene index fossil Ammoelphidiella antarctica Conato et Segre, 1974 indicates a lower age limit of latest Pliocene or earliest Pleistocene age. The upper age limit of the formation has not been established. An encrusting, unilamellar, colony of the bryozoan Escharella Gray, 1848 has been found on the one of erratics from the Weddell Sea Formation. This is the first fossil record of this genus in Antarctica.