Full Breakdown
Revised Age and Formation of Victoria’s Twelve Apostles
4/25/2026, 9:16:06 AM
New Age Range and Formation Process
University of Melbourne geologists have dated the Twelve Apostles to 8.6–14 million years, revising earlier 7–15 million estimates. Tectonic uplift and tilting raised the limestone, and wave erosion after the last glacial maximum (?20 000 years ago) carved the sea stacks.
Stratigraphic Sequence
The cliffs have three units. Basal Gellibrand Marl (15–14 million years) underlies the Port Campbell Limestone, which occurs as a grey, clay-rich layer (14–11.6 million) and a yellow, shallow-water layer (11.6–8.6 million). The top is capped by iron-rich Hesse Clay deposited after uplift stopped.
Research Team and Techniques
Lead author Associate Professor Stephen Gallagher oversaw field mapping, high-resolution photography, gamma-radiation measurements and microfossil analysis. Foraminiferal assemblages gave biostratigraphic ages cross-checked with radiometric data. Unpublished 1960s samples from Clifford Mallet and input from Dr Matthew McCurry (Australian Museum), Dr Erich Fitzgerald (Museums Victoria) and geologist Milo Barham (Curtin) were also incorporated.
Chronology and Climate Significance
- Age range: 8.6–14 million years (Miocene).
- Final sea-stack shaping occurred within the last 20 000 years.
These dates bracket the Middle Miocene Climatic Transition, offering a climate record that informs modern sea-level and temperature projections.
Official Summaries
Gallagher called the findings “exciting” for precisely dating the formation and creating a climate archive. McCurry called foraminifera a “really useful method” for marine dating. Fitzgerald called the paper “important” for “bookending” the Apostles’ age. Barham praised the detailed coastal mapping, and Mallet’s archived samples were essential for extending the temporal framework.
Criticism & Opposition
Some researchers note that, despite the refined ages, the exact timing of the most recent erosional phase is still uncertain. They recommend further dating of the Hesse Clay and post-glacial deposits to resolve remaining ambiguities.
Conflicting Reports & Gaps
Earlier studies gave a broader 7–15 million-year span; the new analysis narrows it to 8.6–14 million years, highlighting a discrepancy in age estimates that future work must address.
Verbatim Quotes
- “We see layers, we see time, we see a history of the Earth” — A/Prof Stephen Gallagher, University of Melbourne
- “If you look closely at the cliffs around the Twelve Apostles today, you can see the limestone layers are not flat but are, in fact, tilted by a few degrees.” — Prof Stephen Gallagher
- “Just as scientists are racing to learn from disappearing glaciers, this study is a reminder that limestone stacks are also fragile archives of past environments,” — Matej Lipar, Anton Melik Geographical Institute
- “Prof Gallagher added, “We are using this ‘window back in time’ to understand where temperatures and sea levels may be heading on our current path of climate change.” — Assoc Prof Stephen Gallagher
Next Steps
Gallagher intends to extract a high-resolution climate record from the middle limestone layer to link Miocene temperature shifts with present-day climate trajectories before further erosion removes the remaining stacks.
