Welcome to the rugged landscapes of SE-Scotland, where time has etched its story into the very rocks beneath our feet. During a recent field trip as part of the EGT-TWINN project annual meeting in Edinburgh, we explored the geological marvels of Siccar Point and Pease Bay. These outcrops not only showcase the fascinating geology of the region but also offer a glimpse into the Earth's ancient past.
To understand the geological significance of Siccar Point and Pease Bay, let's first look at the geological map of the area. The region is dominated by the 427-443 million years old Silurian metamorphosed rocks. These are at places unconformably overlain by significantly younger Devonian (358-383 million years old) and Carboniferous strata (307 - 383million years old).
Edinburgh region sits
within the Midland Valley of Scotland – a major regional tectonic fold. The
valley is bounded by the metamorphic rocks (green and purple regions on the
map) of the Scottish Highlands to the North and the Southern Uplands to the
South and is divided from these areas by major tectonic faults from both sides.
Click on the link here to go to the British Geological Survey maps repository: HTTPS://MAPAPPS2.BGS.AC.UK/GEOINDEX/HOME.HTML?_GA=2.159066042.1889793242.1706628915-1681215430.1706628915
The Midland Valley of
Scotland formed due to tectonic activity during the Caledonian Orogeny – a mountain-building event around 400-500 million
years ago.
The rocks underlying the Midland Valley are dominantly of Carboniferous and Devonian age. During the Devonian period, Scotland lay just south of the equator, giving this region a hot and dry climate with seasonal rains. In the Carboniferous, an equatorial seaway opened to the south, which changed the climate to tropical, giving way to luscious swampy forests and coral reefs. The latter later gave rise to the formation of coal and oil shales.
Siccar Point, located on Scotland's southeast coast, is a global geological site due to its superb exposure to Silurian-Devonian unconformity – a significant several hundred million-year geological gap in time. The unconformity is observable at the rock face at the lower part of the section, where horizontal layers of Devonian Old Red sandstone overlie the vertically tilted and folded Silurian rocks. This geological contact was first described in 1788 by James Hutton – the father of modern geology. The site is protected as a Scheduled Ancient Monument, recognising its scientific, historical and educational importance.
The same
Upper-Devonian Old Red sandstones are better accessible at the Pease Bay outcrop, just a few
kilometres from the Siccar Point outcrop. The sandstones have not witnessed
notable tectonic or metamorphic deformation and present an
excellent opportunity to study various riverine sedimentary structures of that
time.
The Stratheden Group, formally known as the Old Red Sandstone (ORS) is a geological unit that was deposited when the climate and landscape of Scotland was very different from today. It is composed of sandstones, siltstones, mudstones, and conglomerates. All these were deposited in various environments, including river systems and lakes, in an arid desert with little vegetation.
All in all, we got a short but very inspiring glimpse into Scottish geology during this 1-day visit to Siccar Point and Pease Bay. This visit only increased our interest and desire to revisit Scotland for significantly longer and more meaningful geological tours. There is geologically much to learn and a lot to see in Scotland.