A unique, far-travelled graptolite-bearing erratic pebble from the Lowestoft Till (Quaternary: Anglian Stage) of North Lopham, Norfolk

An erratic chert pebble discovered on an exposure of the Lowestoft Till (Anglian Stage, Pleistocene) of North Lopham, Norfolk, UK, contains three-dimensionally preserved, silicified graptolites in a mode of preservation not known in the UK. The graptolites are Monograptus parapriodon , Monograptus priodon , Monoclimacis linnarssoni and an undetermined retiolitid, that indicate the Oktavites spiralis Biozone (mid-late Telychian, Late Llandovery, Silurian) age. The graptolites are associated with organic-walled microfossils, some containing internal bodies. The combination of lithology, preservation and low thermal maturity seem to exclude a British origin. The closest comparison is with Silurian chert pebbles in Miocene and Pleistocene gravels in central Germany, thought to be derived from bedrock in the Frankenwald region of Thuringia. A conjectured natural transport vector for this pebble involves drainage along the proto-Rhine system flowing into early/mid Pleistocene North Sea deltaic/marine deposits, with subsequent glacial transport to Norfolk. The possibility of an anthropogenic vector is also considered, but dismissed.