The Oligocene Epoch: Cooling Climates and Continental Transformation
The Oligocene Epoch marks a crucial turning point in Earth’s history — a time when the planet shifted from the warm greenhouse world of the early Cenozoic to the cooler icehouse conditions that shaped modern ecosystems. Spanning from approximately 33.9 to 23 million years ago, the Oligocene represents the final epoch of the Paleogene Period, preceding the Miocene in the Neogene.
Globally, this was an era of major climate cooling, glaciation in Antarctica, and evolutionary innovation. It was during the Oligocene that mammals diversified following the extinction of earlier species, and the first ancestors of many modern groups — including primates, horses, elephants, and whales — appeared.
For Australia, the Oligocene was a time of profound geological isolation and transformation. As the continent continued to drift northward away from Antarctica, the climate began to dry, volcanic activity reshaped Victoria’s landscape, and the flora and fauna adapted to increasingly seasonal environments.
Global Geological and Tectonic Activity
Continental Positions and Ocean Currents
During the Oligocene, Earth’s continents approached their modern configurations (Scotese, 2015):
Australia and Antarctica separated, forming the Southern Ocean and allowing the Antarctic Circumpolar Current (ACC) to develop.
This event marked the onset of permanent Antarctic glaciation, drastically cooling global temperatures (Zachos et al., 2001).
Africa and Eurasia began to converge, setting the stage for the uplift of the Alps and Himalayas.
North America and Europe were separated by widening Atlantic waters, while the Tethys Sea continued to close.
Volcanism and Erosion
Volcanic activity occurred across many regions, including southeastern Australia, where early basaltic flows laid down the foundations for Victoria’s later volcanic plains (Joyce, 2010).
Sedimentary basins formed along Australia’s southern margin — including the Otway, Gippsland, and Murray Basins — recording marine transgressions and regressions throughout the epoch (McGowran et al., 2004).
Climate: From Greenhouse to Icehouse
The Oligocene is often described as the time when Earth cooled into its modern climate system.
Early Oligocene
Temperatures dropped sharply following the Eocene–Oligocene transition, about 34 million years ago.
The formation of the Antarctic ice sheet caused global sea levels to fall.
Polar regions developed permanent ice, while subtropical areas became drier and more seasonal.
Late Oligocene
Global cooling stabilised, but periodic warming occurred during short interglacial intervals.
Increased ocean circulation — especially the newly formed ACC — distributed cold water around the planet, maintaining lower temperatures.
In Australia, this climatic shift resulted in the decline of tropical rainforests and the spread of open forests and woodland environments, setting the evolutionary stage for the modern Australian flora.
Flora and Vegetation Changes
Australia’s Botanical Transition
Fossil pollen and plant remains from the Oligocene (notably in the Otway and Gippsland Basins) show that rainforests still covered much of southern Australia, but eucalypts and casuarinas began to appear (Christophel & Greenwood, 1989).
This period marks the origin of sclerophyll plants — those with hard, dry leaves adapted to seasonal drought and nutrient-poor soils.
The retreat of rainforest and the expansion of open habitats mirrored global trends.
Global Patterns
In North America and Eurasia, grasslands began to form, although they would not dominate until the Miocene.
Evergreen and deciduous forests adapted to cooler, more variable climates.
Faunal Evolution
Global Context
Mammals diversified rapidly, evolving toward modern forms.
Early ancestors of elephants (proboscideans), horses, and canids (dogs) appeared.
Whales evolved from coastal species into fully oceanic forms.
Early primates adapted to open woodland life, setting the stage for later hominid evolution.
Australia
The Oligocene saw the rise of distinctive marsupial megafauna and the beginnings of modern Australian lineages (Archer & Hand, 2006).
Wombat-like and kangaroo-like forms appear in Oligocene fossil beds.
The ancestor of the thylacine (Tasmanian tiger) dates to this period.
Early possums and koalas developed in forested regions.
Monotremes, such as the platypus and echidna, were already present and adapted to cooler, wetter southern climates.
Marine Life
Marine sediments in Victoria record Oligocene whales, sharks, and invertebrates.
The Otway and Murray Basins preserve coral and mollusc fossils indicating warmer seas prior to late Oligocene cooling.
The Oligocene in Victoria
Geology
In western Victoria, early volcanic activity began forming lava plains that would expand through the Miocene and Pliocene (Joyce, 2010).
Marine transgressions flooded parts of the Otway and Bellarine regions, leaving behind limestone and shell deposits visible today in cliffs and coastal formations.
Inland Victoria began to uplift and erode, giving rise to early drainage systems that evolved into the Barwon and Moorabool Rivers.
Palaeoecology
Fossil pollen and plant impressions from sites like Torquay and Cape Otway indicate mixed rainforest and dry forest ecosystems (Christophel & Greenwood, 1989).
The region supported diverse marsupial fauna, suggesting a mosaic of habitats — from wet forests near the coast to open woodland inland.
Global and Evolutionary Significance
The Oligocene represents the pivot point in Earth’s climate history — where permanent polar ice formed, atmospheric CO₂ declined, and ecosystems adapted to colder, drier conditions.
These changes directly influenced the evolution of modern mammalian and plant lineages.
The restructuring of ocean currents shaped weather systems that persist today.
In Australia, isolation led to the independent evolution of the continent’s distinctive biodiversity.
Connection to Aboriginal Country and Deep Time
Though Aboriginal peoples arrived millions of years after the Oligocene, their Dreaming stories often reference geological transformations originating in this era — the shaping of rivers, mountains, and volcanic landscapes (Rose, 1996; Neale, 2017).
Places such as Budj Bim, formed by later volcanic events rooted in Oligocene–Miocene geology, remain sacred to the Gunditjmara people, reflecting a living connection to deep Earth processes.
This demonstrates that Indigenous knowledge systems preserve a deep-time awareness of geological change, integrating creation stories with the natural record of Earth’s evolution.
Conclusion
The Oligocene Epoch was a period of profound global transformation — geologically, climatically, and biologically. It marked the transition from a lush, tropical Earth to one defined by cooler temperatures, polar ice, and evolving modern ecosystems.
For Victoria and Australia, the Oligocene laid the foundations of today’s environment: the birth of volcanic plains, the retreat of rainforests, and the emergence of flora and fauna uniquely adapted to isolation and aridity.
This epoch, preserved in both fossil evidence and living cultural memory, reminds us of the Earth’s capacity for renewal — and of humanity’s deep, enduring connection to an ever-changing planet.
References
Archer, M., & Hand, S. (2006). The Evolution of Australia’s Fauna. Sydney: UNSW Press.
Christophel, D. C., & Greenwood, D. R. (1989). “Changes in vegetation and climate through the Tertiary of southeastern Australia.” Review of Palaeobotany and Palynology, 58, 99–129.
Joyce, E. B. (2010). The Western Victorian Volcanic Plains: A Field Guide to the Newer Volcanics Province. Geological Society of Australia.
McGowran, B., Li, Q., Cann, J., & Padley, D. (2004). The Cenozoic of the Australian Southern Margin: Evolution of a Rifted Continent. Journal of Australian Earth Sciences, 51, 125–145.
Neale, M. (2017). Songlines: The Power and Promise. Canberra: National Museum of Australia.
Rose, D. B. (1996). Nourishing Terrains: Australian Aboriginal Views of Landscape and Wilderness. Canberra: Australian Heritage Commission.
Scotese, C. R. (2015). The Paleomap Project: Paleogeographic Maps of the Oligocene Epoch. University of Texas.
Zachos, J., Pagani, M., Sloan, L., Thomas, E., & Billups, K. (2001). “Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present.” Science, 292(5517), 686–693.
Written, Researched and Directed by James Vegter 07/10/2025
Magic Lands Alliance
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