New exposure of the Cretaceous–Paleogene unconformity and Paleocene–Eocene pebble bed in the Paleogene outlier at Collier's End, Hertfordshire, UK

The Paleogene outlier at Collier's End, Hertfordshire lies on the northern rim of the London Basin. This small outlier has archaeological and geological significance. Silica-cemented concretions of Hertfordshire Puddingstone lie within a regionally mappable pebble bed. The first discovery of a Roman quarry to recover puddingstone for manufacture of querns was made in the outlier. A rare complete section from the Chalk Group up through the Paleogene was temporarily exposed in 2021 and is recorded here. The Paleogene shows features that may be associated with the Paleocene–Eocene Thermal Maximum (PETM). The chalk in the new exposure is Late Coniacian. This age provides further evidence of relatively deep erosion of the chalk in this area, as erosion of chalk at the crest of a regional dome preceded advances and retreats of the western shore of the Paleogene North Sea. These events may be linked to the early development of the Icelandic mantle plume.