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The Cretaceous–Paleogene (K–Pg) mass extinction event occurred 66 million years ago, the most recent of the ‘Big Five’ extinction crises of the last 540 million years. This event had a profound effect on both life and the broader Earth system, with the extinction of up to 75% of life. Despite years of detailed research, debate continues as to the nature and timing of the extinction. Ideas for an abrupt crisis, triggered by bolide impact at Chicxulub in the Gulf of Mexico, contrast with those suggesting a more gradual extinction, involving volcanism from the Deccan Traps Large Igneous Province in India and/or climatic changes. Evidence from the high latitudes has been used to suggest that the fossil record from Antarctica is incompatible with models for a single, sudden event, and that extinction intensity declined at high latitudes. This thesis presents a detailed study of extensive fossil and sediment collections from the highest southern latitude onshore outcrop containing the K–Pg transition; the highly expanded and fossiliferous López de Bertodano Formation of Seymour Island, James Ross Basin, located at 65°S today, and during the Cretaceous. New biostratigraphic and diversity data for the molluscan (bivalves, gastropods, cephalopods) faunas of the López de Bertodano Formation, and geochemical datasets (seawater sulphur and pyrite sulphur isotopes) are compared to published records, and evidence for palaeoenvironmental change. They suggest a single, rapid extinction event coincident with the K–Pg boundary, with no precursor decline. The magnitude of the extinction in Antarctica is also consistent with lower latitudes, suggestive of a global, catastrophic trigger for the K–Pg extinction, such as bolide impact. Sulphur isotope data suggest the K–Pg sulphur cycle was able to respond to rapid environmental changes before, and after the K–Pg mass extinction. A decoupling of the carbon and sulphur cycle occurred during the latest Cretaceous, but productivity collapse after the K–Pg extinction also affected the sulphur cycle. The recovery to pre-extinction values was achieved on the same timescale as carbon cycle and initial ecological recovery, suggesting close geosphere-biosphere links at this time.

During the green house world of the Paleocene, Antarctica was covered in extensive forests, even though the continent was situated over the South Pole. Fossil wood is abundant in the marine sequences of Seymour Island, Antarctica. Originating from forests that once grew on a volcanic arc now represented by the Antarctic Peninsula. This research presents a detailed study of the forests and climates of Antarctica primarily using a new assemblage of fossil wood and palynomorphs, directly tied to a sedimentary sequence (K/Pg boundary to Late Paleocene in age) on Seymour Island, which has allowed for a more rigorous interpretation of the composition and structure of the Antarctic Peninsula forests and the climates under which they grew. Tree types identified from fossil wood include: Agathoxylon, Phyllocladoxylon, Protophyllocladoxylon, Podocarpoxylon/Cupressinoxylon, Nothofagoxylon, Weinmannioxylon, Myrceugenelloxylon and Antarctoxylon. Their nearest living relatives (NLR) are found growing in warm to cool temperate Southern Hemisphere forests. Palynomorphs revealed diverse Podocarpaceae including Lagarostrobos franklinii (Phyllocladidites mawsonii) and shrubby angiosperm taxa such as Proteaceae, as well as ferns and mosses. Collective analysis of taxomomy, wood preservation, sedimentology and NLRs indicate that the lowland forests were similar to the cool temperate mixed Nothofagus forests of New Zealand and Thamnic/Implicate forests in Tasmania. Upland floras may have resembled Araucaria – Nothofagus woodlands found in cool temperate Chile today. Coexistence Analysis indicates marginally warm to cool temperate climates with sufficient rainfall for tree growth. Analysis of angiosperm anatomy suggests sufficient water availability. Mean growth ring analysis suggests a trend towards cooler climates from the Early to the Late Paleocene. However, the majority of trees suggest growth under a fluctuating climate. For the first time specific gravity (SG) has been calculated for fossil wood from Antarctica and has provided further insight into the ecology and growth conditions of the trees. Narrow values of SG (0.50 – 0.80) are indicative of a temperate climate in the Paleocene of Antarctica.