Recent detailed mapping, section logging and an improved understanding of the geological evolution of the Antarctic Peninsula provide a robust framework for an improved lithostratigraphic subdivision of the Latady Basin, eastern Ellsworth Land. Within the Latady Basin we recognize two main groups: Ellsworth Land Volcanic Group and Latady Group. The focus of this paper is the Latady Group, which is formally subdivided into five formations: Anderson Formation, Witte Formation, Hauberg Mountains Formation, Cape Zumberge Formation and Nordsim Formation. Middle Jurassic, shallow marine deposits of the Anderson Formation are overlain by quiet anoxic deposits assigned to the Witte Formation. The start of the Late Jurassic is marked by the deposition of higher energy deposits of the Hauberg Mountains Formation, subdivided into three members (Long Ridge, Mount Hirman and Novocin members) that reflect varying lithological and environmental characteristics. Thermal subsidence during the latest Jurassic led to deposition of the basinal Cape Zumberge Formation, while uplift of an active continental arc along the Antarctic Peninsula led to deposition of the terrestrial Nordsim Formation in the latest Jurassic to earliest Cretaceous. The evolution of the Latady Basin reflects early extension during Gondwana break-up, from the Early Jurassic to earliest Cretaceous, and is consistent with a shift in the underlying forces driving extension in the Weddell Sea area from intracontinental rifting related to a mantle plume, to active margin forces in response to subduction.

The Jurassic Mount Poster Formation of eastern Ellsworth Land, southern Antarctic Peninsula, comprises silicic ignimbrites related to intracontinental rifting of Gondwana. The identification of less voluminous basaltic and sedimentary facies marginal to the silicic deposits has led to a reclassification of the volcanic units into the Ellsworth Land Volcanic Group. This is formally subdivided into two formations: the Mount Poster Formation (silicic ignimbrites), and the Sweeney Formation (basaltic and sedimentary facies). The Mount Poster Formation rhyolites are an intracaldera sequence greater than 1 km in thickness. The basaltic and sedimentary facies of the Sweeney Formation are consistent with deposition in a terrestrial setting into, or close to, water. The geochemistry of the Mount Poster Formation is consistent with derivation of the intracaldera rhyolites from a long-lived, upper crustal magma chamber. The basalts of the Sweeney Formation are intermediate between asthenosphere- and lithosphere-derived magmas, with little or no subduction-modified component. The basalt could represent a rare erupted part of the basaltic underplate that acted as the heat source for local generation of the rhyolites. U–Pb ion microprobe zircon geochronology of samples from the Mount Poster Formation yield an average eruption age of 183.4±1.4 Ma. Analysis of detrital zircons from a Sweeney Formation sandstone suggest a maximum age of deposition of 183±4 Ma and the two formations are considered coeval. In addition, these ages are coincident with eruption of the Karoo-Ferrar Igneous Province in southern Africa and East Antarctica. Our interpretation of the Ellsworth Land Volcanic Group is consistent with the model that the Jurassic volcanism of Patagonia and the Antarctic Peninsula took place in response to intracontinental extension driven by arrival of a plume in that area.

The leaf longevity and seasonal timing of leaf abscission within a plant community is closely related to climate, a phenomenon referred to as leaf phenology. In this paper the leaf phenology of some mid-Cretaceous (late Albian) forests which grew at latitude of 75° S on Alexander Island, Antarctica, is analysed. Five independent techniques for determining leaf longevity are applied to the fossil remains of each of the canopy-forming trees. These techniques utilize: (1) the anatomical character of growth rings in trunk woods, (2) leaf trace persistence in juvenile branch and stem woods, (3) leaf physiognomy, (4) comparison with nearest living relatives, and (5) leaf taphonomy. The application of techniques 1–5 suggests that the araucarian and podocarp conifers, which comprised more than 90% of the canopy-forming vegetation, were evergreen with leaf retention times in excess of 5–13 years. The application of techniques 3–5 to rare taxodioid conifers indicates the existence of both evergreen and deciduous habits in this group, whilst both ginkgos and taeniopterids, which are locally abundant, are interpreted as possessing a deciduous habit. The polar forests of Alexander Island were therefore dominantly evergreen. Preliminary analysis of five other mid-Cretaceous polar forests suggests the presence of dominantly evergreen vegetation in Australia and Antarctica, and mixed evergreen–deciduous vegetation in Alaska, northern Russia and New Zealand. Cold month mean temperature probably exerted the largest influence on the leaf phenology at each of these forest sites.

The northern, James Ross Island region of the Larsen Basin, on the eastern, back-arc margin of the Antarctic Peninsula magmatic arc, includes one of the thickest and most complete Upper Cretaceous sedimentary successions exposed in the Southern Hemisphere. However, the southern part of the basin remains poorly known, mainly owing to inaccessibility and lack of exposure. Table Nunatak, an isolated, 1-km-long, 400-m-wide outcrop at the tip of Kenyon Peninsula, is the only known exposure of Upper Cretaceous or younger strata in this region. The 62-m-thick succession exposed there is assigned to the newly defined Table Nunatak Formation. It consists mainly of sharp-based, amalgamated beds of fine-grained sandstone up to 2.8 m thick, with subordinate intervals of intensely bioturbated mudstone. Wave ripples are present at some levels, and locally developed swaley cross-stratification provides evidence for storm-generated combined-flow deposition. However, most sandstone beds appear to be internally structureless apart from normal grading, and are interpreted as the direct suspension deposits of highly sediment-charged storm- and/or flood-related flows. The succession represents relatively nearshore deposition, probably at the mouth of a river or deltaic distributary channel. Charcoalified plant debris, abundant at the tops of some sandstone beds, suggests a periodically wildfire-swept hinterland forested largely by coniferous trees. Dinoflagellate cyst assemblages indicate a late Santonian age, and suggest correlation with the basal part of the Lachman Crags Member of the Santa Marta Formation (Marambio Group) on James Ross Island. Palaeocurrents, sandstone petrography and the high sediment supply rate proposed for the Table Nunatak Formation, suggest a relatively high-relief source area to the west, with large-scale erosion of granitoid plutons and metamorphic rocks, possibly related to arc uplift during a mid-Cretaceous compressional episode. The formation is evidence of a major southward extension of the Upper Cretaceous strata exposed in the northern Larsen Basin, and suggests lateral continuity of shallow-marine deposition for at least 500–600 km along the Weddell Sea margin of the Antarctic Peninsula in Santonian times.