For most geologists, the northeast of Scotland will be associated with a dominance of granites and gneiss, as these Caledonian rocks make up the majority of the exposed geology.
However, there are some pockets of “young” preserved sedimentary rocks in places, and one of those is the Rhynie Basin, near the village of Rhynie.
This remnant Early Devonian intra-montane basin is only about 15 kilometres in length and up to two kilometres wide. Fault-bounded in the west, the sedimentary succession bears the resemblance of a pull-apart basin that formed when the Caledonian Mountain Belt collapsed.
What makes the Rhynie Basin literally a world-famous place is the so-called Rhynie Chert
Due to tectonic activity in Early Devonian times, a hydrothermal system developed along the western faulted margin of the Rhynie Basin, leading to a series of hot springs. Taking place at a time when life started to explore the land, the preservation of fossils by the siliceous precipitates of the hydrothermal system now forms a unique archive to further study this important phase in earth’s evolutionary path.
The significance of the Rhynie chert (amorphous quartz that precipitated from the hydrothermal waters once at surface) has been realised by academics for a long time. As early as the 1917, publications on the fossilised plants started appearing. It was the ability to study the three-dimensional structure of the cellular structure of the plants that made this site so critical and it continues to be to today.
The peak of interest and work done on the Rhynie hot spring system probably dates back to the early 2000’s when over forty delegates attended an international conference organised by Aberdeen University, for which the late Nigel Trewin was one of the main driving forces.
At the time, several trenches were dug and at least three boreholes were drilled to further study the up to 38 individual chert beds that intercalate a series of fluvial overbank and lacustrine sediments deposited on the Early Devonian alluvial plain.
A potential world heritage site
Much more recently, an article in the P&J further highlighted the continued significance of the area. Christine Strullu-Derien, who works with the National History Museum in London, has emphasised that it’s not only the plants, but also the preserved animals, fungi and bacteria that make this site unique. She therefore suggested this site to be shortlisted as a world heritage site.
More needs to be done
I caught up with Francis Buckley late last year, to see what the current status is of the area. Francis is a geophysicist who has worked in the site survey industry for many years. He is also a keen geologist and being a resident of Rhynie he has always had a keen interest in the site.
Currently under supervision by NatureScot (former Scottish Natural Heritage), the area looks rather dull, especially on a chilly and cloudy November morning. Francis recalls: “a few samples of Rhynie chert were until recently on display in the local school, but these have been removed and are now being kept in a museum depot. It is about time to resurrect the area, especially because there are no natural outcrops, and look at ways to permanently expose it to the public such that people can learn about this valuable piece of Scottish geology and its significance to the world.”
Sources data for featured image:
Scottish Government and SEPA (2014) for the elevation data (Open Government Licence)
British Geological Survey materials (2021) for the basin extent overlay (Open Government Licence)
Ordnance Survey data for map overlay.