Silurian erratic boulder travelling from Thuringia to England

An erratic chert pebble discovered in an exposure of the Pleistocene till in Norfolk, UK, contains graptolites and microfossils preserved three-dimensionally in silica. Graptolites indicate a Silurian (Llandovery) age. The combination of lithology, preservation, and low thermal maturity seem to exclude a British origin. The closest comparison is with Silurian chert pebbles in Pleistocene gravels, thought to be derived from bedrock of Thuringia, from where it likely migrated with glacial melt to Pleistocene deltaic sediments of the North Sea with subsequent glacial transport to Norfolk.

Illustration: Probable journey of the erratic boulder by rivers from Thuringia (Frankenwald) to the North Sea, and then to England. Palaeogeographic reconstruction for th Pleistocene epoch. Below the pebble itself, with the graptolite visible on the right-hand side.