Abstract
Studying geological records of the Pliocene epoch (5.33–2.58 Ma) provides a critical ana-logue for understanding future climate system responses and Antarctic Ice Sheet (AIS) be-haviour, yet a scarcity of near-field geological data hampers precise reconstructions of Plio-cene ice volume. This study addresses this gap by investigating Pliocene sediments from the Vestfold Hills, East Antarctica, to provide evidence of past ice-free conditions. Sediment cores from Marine Plain (early Pliocene) and Heidemann Valley (late Pliocene) were exam-ined for evidence of soil-forming processes using a suite of techniques. While bulk geochem-ical indices (e.g., Chemical Index of Alteration) and mineral abundance ratios proved insensi-tive to specific soil-forming events, as they reveal only a general weathering signature with-out resolving the specific soil-forming events characteristic of ice-free conditions. Hence, a suite of targeted proxies provided a more detailed paleoenvironmental record.This study focused on frequency-dependent magnetic susceptibility (χfd%) to detect the in situ formation of ultrafine superparamagnetic minerals, iron oxide mineralogy (goethite and hematite) quantified from sediment colourimetry and a Colour Strength Index (CSI) to assess the redox state of the weathering environment, and leachate geochemistry (ICP-MS) to trace elemental mobility. The results reveal two distinct and co-existing paleoenvironmental histo-ries. The Marine Plain sediments exhibit consistently high χfd% values (up to 3.08%), signifi-cant hematite enrichment (high CSI, up to 30.5), and pervasive mobilization of aluminium and iron, indicating the presence of a thick, continuous paleosol formed during a prolonged period of evident oxidizing, and acid-sulphate weathering on a stable subaerial landscape. In contrast, the Heidemann Valley sediments are dominated by a physical weathering signature (low χfd%, less than 0%) and a glaciomarine salt chemistry, except for a single, discrete paleosol horizon identified by a sharp, simultaneous signature in all three pedogenic proxies and a corresponding spike in Al and Fe mobilization.
These findings provide evidence for contrasting Pliocene environments: a stable, oxidizing terrestrial landscape at Marine Plain versus a dynamic glaciomarine setting at Heidemann Valley that experienced only transient exposure. This demonstrates that the East Antarctic Ice Sheet margin was highly sensitive to Pliocene warmth, capable of supporting both sustained soil formation and rapid glacial fluctuations, thereby providing ground-truth data for ice sheet models and improving our understanding of past sea-level changes.
| Date of Award | 2026 |
|---|---|
| Original language | English |
| Supervisor | Duanne WHITE (Supervisor) |
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