Mull – Ardtun leaf beds

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Exceptional fossil leaves from Ardtun were brought to the attention of the scientific world by the 8th Duke of Argyll (1823 – 1900) in 1850, after having been discovered some years earlier by a local of the area. The Duke, following further investigation, passed the leaves to Professor Edward Forbes (1815 – 1854) for further study. As part of his work, Forbes assigned them to the early Palaeogene and since then they have been dated to around 58 million years old.

Ardtun SSSI, Mull - the location of the Ardtun Leaf beds, a fossil-bearing sedimentary sequence sandwiched between lava flows. © Scottish Natural Heritage.
Ardtun SSSI, Mull – the location of the Ardtun Leaf beds, a fossil-bearing sedimentary sequence sandwiched between lava flows. © Scottish Natural Heritage.

The beds, exposed at the mouth of Loch Scridain, Mull, exist in a sedimentary unit near the base of a lava sequence. Three distinct beds have been identified within the unit, which also exhibits clays, sandstones and gravels. The leaves are considered to have fallen into the peaceful waters of a lake, but the presence of the sand and gravels suggests a fluvio-lacustrine environment. The climate at the time of formation is considered to have been fairly warm and humid.

The preservation of the leaves is excellent, with some being described as “retaining almost the colour of the dead leaves themselves”. Plants found include Pteridophyta, Gymnosperms (including the leaves of Ginkgo, the large Platanus hebridica and coniferous remains) and Angiosperms. The largest proportion of leaves have come from deciduous trees such as Platanus, Corylites and Quercus. Other fossilised remains include fruits, plant stems, ferns, insects and freshwater molluscs.

The sedimentary sequence marks a quiet period during eruptions from the Palaeogene Mull volcanic centre. Other sedimentary rocks are found elsewhere throughout the volcanic sequence.

Note: The Mull volcanic centre forms part of the North Atlantic Palaeogene Igneous Province, along with the other centres of Skye, Arran, Ardnamurchan, Rum and St. Kilda.

Further reading:

Bailey, E.B. & Anderson, E.M. 1925. The Geology of Staffa, Iona & Western Mull (Memoirs of the Geological Survey, Scotland). His Majesty’s Stationery Office, Edinburgh.

Emeleus, C.H. & Gyopari, M.C. 1992. British Tertiary Volcanic Province, Geological Conservation Review, Series No. 4. Joint Nature Conservation Committee, Peterborough, 259 pp.

Emeleus, C.H & Bell, B.R. 2005. British regional geology: the Palaeogene volcanic districts of Scotland (Fourth edition). (British Geological Survey, Nottingham.

Stephenson, D. 2005. Mull and Iona – A Landscape Fashioned by Geology. Produced by: Scottish Natural Heritage & British Geological Survey.