The Paleocene - Eocene mangroves of southeastern Australia: spatial and temporal occurrences across four geological basins

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 649; p. 112317
• Main Authors: Holdgate, Guy R., Sluiter, Ian R.K., Clowes, Chris D., Reichgelt, Tammo, Frieling, Joost
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2024
• Subjects: Mangroves; Paleocene-Eocene palaeoclimates; Palynology; PETM; SE Australia; Mangroves; Palynology; PETM; SE Australia; Paleocene-Eocene palaeoclimates
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2024.112317

The advent of the Paleocene-Eocene Thermal Maximum (PETM), a ∼ 200 kyr period of global warming ca. 56 Ma, caused sea-levels to rise, transgressing near-coastal environments in southeastern (SE) Australia over >55,000 km2. During the PETM, warming tropical climates may have extended south to ≥60°S paleolatitude. The PETM in SE Australia is corroborated primarily by stable carbon isotope chemostratigraphy and detailed palynology records in four geological basins. Previous work showed that, in addition to the globally recognised carbon isotope excursion, the PETM interval in coastal SE Australia can be identified using the dual occurrence of the tropical mangrove Nypa palm pollen (Spinizonocolpites prominatus) accompanied by thermophilic marine dinoflagellate cysts (mainly Apectodinium hyperacanthum). We here document a total of twenty-six Gippsland Basin wells that record this Nypa-A.hyperacanthum association in the earliest Eocene Kingfish Formation (Lower Malvacipollis diversus Zone). In the Bass Basin, eight wells record Nypa-A.hyperacanthum association within the Eastern View Group basal Koorkah Formation, or lower part of the Lower M. diversus Zone (earliest Eocene). In the Bass Basin a further thirteen wells with Nypa occurrences near the top of the Cormorant Formation are found, which might be associated with the longer-term warmth of the Early Eocene Climatic Optimum (EECO, ∼53–49 Ma). Government bores and petroleum wells across the Otway Basin record the Nypa-A. hyperacanthum PETM association within the Pember Mudstone Lower M. diversus Zone in twenty-one bores. Nine horizons with Nypa occurrences occur within the Burrungule Member (EECO) at the top of the Dilwyn Formation. In western Tasmania, Nypa occurs in the Sorell Basin and Macquarie Harbour area within the Lower M. diversus Zone. Together, these observations show the remarkable extent of the mangrove-coasts that were established across the mid-high paleolatitudes in SE Australia during the warmest intervals of the Cenozoic, the PETM and EECO.
•In 56 Ma SE Australia, 5 m sealevels flooded >55,000km2 of near-coastal environments.•PETM megathermal biota are found at localities down to ∼65°S paleolatitude.•The PETM is identified in the Gippsland, Bass, Otway and Sorell basins.•The PETM contains mangrove Nypa palm pollen (Spinizonocolpites prominatus).•Thermophylic marine dinoflagellates include Apectodinium hyperacanthum.