Heat and dust

• Main Author: Muir-Wood, Robert
• Format: Book Part
• Language: English
• Published: Oxford University PressOxford 2024
• Subjects: Greenland; Rockall Bank
• Online Access: http://dx.doi.org/10.1093/oso/9780198871620.003.0005; https://academic.oup.com/book/chapter-pdf/58292275/oso-9780198871620-chapter-5.pdf

Abstract After the western Britain and Ireland volcanoes and dykes became extinct an even bigger outburst of volcanic activity, to the west of the Rockall Bank, heralded the formation of a new plate boundary spreading ridge separating Greenland from Europe. Initially this volcanic activity was subaerial and the eruptions created ashfall downwind. The ash comprised fragments of volcanic glass, which exposed to water decayed into clay minerals. Across Britain the ash was transported by rivers to the southeast where it accumulated in the London Clay formation on which London is founded. This volcanic sourced clay was fired to manufacture the bricks from which, prior to the arrival of railways, much of the building stock of the city was built. An episode of global warming (‘the Paleocene/Eocene thermal maximum’) accompanied the release of hydrocarbons in the creation of the new plate boundary. Combined with the acidification caused by the decomposition of the ash, surface sands were turned into a hard ‘silcrete’ rock. As the underlying clays and sands were washed away, the silcrete layer foundered into slabs, known as sarsens. Suitably shaped sarsen slabs were revered by neolithic and bronze age communities as the bodies of ancestors while some of the largest of all slabs were transported tens of kilometres in the construction of Stonehenge. In Hertfordshire the silicification of gravel created puddingstone, contemporary with sarsen, and mined and carved by the Romans for manufacturing kitchen querns for grinding wheat. Sarsens are testimonial to the strongest episode of global warming in the last 66 million years, which resulted in the extinction of many species.