the island that roofed the world travel and nontravel Tim Ingleby 1.2 billion years ago: rift and drift
geology’ time shipping quarries
Fragments of the supercontinent Columbia (or Nuna) converged in the southern hemisphere to form a new supercontinent, Rodinia. It contained almost all the landmasses on Earth. Though in existence for some 450 million years, Rodinia was never geologically stable. Plumes of magma rose from the Earth’s mantle fracturing the rock beds and creating basaltic dikes. At the same time, vast piles of sediments from erosion, weathering, dissolution, precipitation and lithification accumulated in the seas around Rodinia. Gradually Rodinia rifted into individual tectonic plates that drifted apart. One of these plates was the new continent of Laurentia. Sediment continued to form around its mass as it travelled slowly northwards over the next 100 million years. Once at the Equator, the continents of Laurentia, Baltica and the southern supercontinent Gondwana converged upon one another. Laurentia and Baltica collided head on, causing their rocks to become deeply buried, heated and recrystallised. New minerals grew in this metamorphic process. Meanwhile, a sliver of continental crust separated from Gondwana and known as Avalonia docked more gently to the south of Laurentia. The Caledonian orogeny (mountains formed by compression at the margins of colliding plates) is thus formed. After a further 200 million years of tectonic events the orogeny rifted apart forming landmasses that will become proto-North America, Britain and Northern Europe. In 1815, William Smith, took it upon himself to be the first person to map the geology of an entire nation, in his case, Britain. This resulted in ‘A Delineation of the Strata of England and Wales, with Part of Scotland; Exhibiting the Collieries and Mines, the Marshes and Fen Lands Originally Overflowed by the Sea, and the Varieties of Soil According to the Variations in the Substrata, Illustrated by the Most Descriptive Names’ , a title much less punchy than the map’s graphic qualities. It suggests a border between England and Scotland that is not only political but also geological which later maps in Smith’s stead will make yet more distinct. Described as the ‘Magna Carta of Geology’ it illustrates how the confluence and disaggregation of landmasses over many millions of years resulted in the quirk that today a country such as Scotland can be geologically more closely related to places now thousands of miles away, such as Greenland or the Appalachian range of North America, than an immediate neighbour such as England.
Tim Ingleby
Laurentian geology, 2023
wikimedia
William Smith, Geological Map of Britain, 1815. Detail shows Scotland/England border.
34 on site review 46 :: travel
Made with FlippingBook interactive PDF creator