A 2.7 m thick mid-Holocene sedimentary succession composed of alluvial fan and marine beach deposits is exposed at 14.4-17.1 m above sea level (a.s.l.) on the south-eastern coast of Potter Peninsula, King George Island (South Shetland Islands, Antarctica). The raised marine beach deposits contain a subfossil assemblage that includes remains of Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins, skua (Catharacta sp), seals (elephant seal Mirounga sp), and seaweed fragments. The palaeontological and palaeogeographical evidence allows us to infer that penguin rookeries were active on high cliffs of the Potter Peninsula during the marine beach sedimentation, which is dated to c. 4540-4450 reservoir-corrected 14 C yr BP on the basis of radiocarbon dating on penguin bones. The data presented in this paper are in agreement with the Holocene palaeoenvironmental chronology known from Potter Peninsula, and suggest that marine birds and seals inhabited the coastal areas of King George Island probably during a midHolocene period of seasonally open marine conditions, which may coincide with a cooling period around Antarctica estimated from ice core records between 8000-4000 yr BP that preceded the "climate optimum" in the Antarctic Peninsula (4000-3000 yr BP).

Knowledge of the late Miocene–Pliocene climate of West Antarctica, recorded by sedimentary units within the James Ross Island Volcanic Group, is still fragmentary. Late Miocene glaciomarine deposits at the base of the group in eastern James Ross Island (Hobbs Glacier Formation) and Late Pliocene (3 Ma) interglacial strata at its local top on Cockburn Island (Cockburn Island Formation) have been studied extensively, but other Neogene sedimentary rocks on James Ross Island have thus far not been considered in great detail. Here, we document two further occurrences of glaciomarine strata, included in an expanded Hobbs Glacier Formation, which demonstrate the stratigraphic complexity of the James Ross Island Volcanic Group: reworked diamictites intercalated within the volcanic sequence at Fiordo Belén, northern James Ross Island, are dated by 40Ar/39Ar and 87Sr/86Sr at c. 7 Ma (Late Miocene), but massive diamictites which underlie volcanic rocks near Cape Gage, on eastern James Ross Island, yielded an Ar–Ar age of <3.1 Ma (Late Pliocene). These age assignments are confirmed by benthic foraminiferal index species of the genus Ammoelphidiella. The geological setting and Cassidulina-dominated foraminiferal biofacies of the rocks at Fiordo Belén suggest deposition in water depths of 150–200 m. The periglacial deposits and waterlain tills at Cape Gage were deposited at shallower depths (<100 m), as indicated by an abundance of the pectinid bivalve ‘Zygochlamys’ anderssoni and the epibiotic foram Cibicides lobatulus. Macrofaunal and foraminiferal biofacies of glaciomarine and interglacial deposits share many similarities, which suggests that temperature is not the dominant factor in the distribution of late Neogene Antarctic biota. Approximately 10 m.y. of Miocene–Pliocene climatic record is preserved within the rock sequence of the James Ross Island Volcanic Group. Prevailing glacial conditions were punctuated by interglacial conditions around 3 Ma.

The first fossils from Antarctica were collected from Seymour Island in December 1892, during the voyage of the Jason under Captain C.A. Larsen. The Swedish South Polar Expedition of 1901–1903, led by Otto Nordenskjöld, proved that there were extensive deposits of fossiliferous Cretaceous and Tertiary sedimentary rock in the James Ross Island area. This was confirmed by later geological mapping (Bibby 1966). Subsequent investigations have led to the establishment of various lithostratigraphic schemes (e.g. Ineson et al. 1986), and interpretation of the sedimentary history in terms of basin evolution (Elliot 1988, Macdonald et al. 1988). Unfortunately, different names have been proposed for the depositional basin, with consequent confusion. The purpose of this note is to review previous usage and propose a new consistent nomenclature for the sedimentary basins east of the Antarctic Peninsula.

Abstract:We present preliminary results of the first detailed surveys of the former Larsen-A Ice Shelf, Larsen Inlet aiid southern Prince Gustav Channel. where disintegration of small ice shelvcs in the past ten years has exposed the seafloor. Glacial troughs in the Larsen-A area, Larsen Inlet and Prince Gustav Channel reach 900-1 100 in depth and have hunitnocky floors. Farther south-cast, the continental shelf is shallower (400-500 in) and its surface is fluted to smooth, with the density of iceberg furrowing increasing towards the shelf edge. Acoustic profiles show a drape of transparent sediment 4-8 m thick in Princc Gustav Channel, thinning southwards. In cores, this drape corresponds to diatom-bearing marine and glacial-marine mud. In the Larsen-A area aiid Larsen Inlet, acoustically opaque sediment includes proximal ice shelfglaciomarine gravelly aiid sandy muds. aiid firm to stiff diamicts probably deposited subglacially. These arc overlain by thin (up to 1.3 in) glacioniariiie muds, locally with distinctivc diatom ooze laminae.

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Jason Peninsula (66°10'S, 61°00'W) is a prominent feature extending some 80 km into the Larsen Ice Shelf from the eastern coast of the Antarctic Peninsula, and consists of widely spaced rock exposures and several ice-domes with elevations up to some 600 m (Fig. 1). The feature was first seen from seaward on 1 December 1893 by Captain C.A. Larsen, who named one of the high summits “Mount Jason” after his ship. Leading the 1902–1904 Swedish Antarctic Expedition, Dr Otto Nordenskjöld observed the area from Borchgrevink Nunatak (66°03'S; 62°30'W) and reported that the summits seen by Larsen were separated from the Antarctic Peninsula. The name “Jason Island” was subsequently adopted for this feature, but in the 1950s researchers belonging to the currently named British Antarctic Survey (BAS) determined Larsen's discovery to be a large peninsula, underlain mainly by calc-alkaline volcanic rocks.

The presence of gaseous hydrocarbons (from methane to n-pentane) in the seabed sediments and the bubbling of methane may suggest the presence of gas accumulations in the substrate of the NW Weddell Sea, Antarctica. The release of methane from the frozen ocean substrate adjacent to Seymour Island would be linked to climate instability during Late Cenozoic, when vast areas of the Antarctic continental shelf were flooded during the marine transgression that occurred . 18,000 years ago, after the Last Glacial Maximum (LGM). As the ice melted, the sea again occupied the regions which it had abandoned. As the transgression was relatively rapid, the sub-air relief was not destroyed but was submerged and the ground had frozen (permafrost) along with it. Thus, the heat flow from the sea to the marine substrate, now flooded, would have destabilized frozen gas accumulations, which were originally formed into terrestrial permafrost during the LGM, similarly to what would have happened in the Arctic.

New structural data from the northern Antarctic Peninsula suggest that reverse faults and folds affecting the Pedersen Nunatak beds of the upper Mesozoic–Lower Cenozoic Larsen Basin succession were produced by transpressional forces acting parallel to the Weddell Sea coast of the Antarctic Peninsula during mid-Cretaceous compression of the Larsen Basin. At Pedersen Nunatak, Larsen Basin rocks are deformed into a series of synclines and anticlines that are cut by reverse faults.