Walton-on-the-Naze Fossil Hunting

1704 – Fossiliferous deposits recorded
Samuel Dale noted fossil-bearing deposits at Walton, providing an early published record of the locality.

1811–1812 – The Crag attracts wider attention
Parkinson described the exposed Crag section, while Sowerby’s work drew attention to its fossil molluscs.

1829–1833 – Charles Lyell studies the section
Lyell visited in 1829 and collected molluscs. He subsequently illustrated the section in the first edition of his Principles of Geology.

1854 – The Eocene succession described
Prestwich published an account of the older sediments beneath the Crag, contributing to the geological interpretation of the cliff.

1859–1866 – A reference locality for the Red Crag
Wood regarded Walton as a characteristic Red Crag section and in 1866 published a list of 118 mollusc species from the site.

1900 – The Waltonian stage
Harmer used Walton as the type locality of the Waltonian, distinguishing its relatively warm-water fauna from younger Crag assemblages farther north.

1931 – An expanded mollusc record
Kendall’s account brought the recorded mollusc fauna close to 300 species, demonstrating the exceptional diversity of the Red Crag at Walton.

1977 – A detailed Eocene bed sequence
George and Vincent published an eleven-unit composite section following a 1976 field meeting, documenting the wood-rich and fossil-bearing horizons of the lower succession.

1982–1984 – Fossil birds formally described
Harrison described several bird remains from Walton, helping establish the site’s importance for early Eocene avian evolution. Some initial identifications were subsequently revised.

1988–1989 – Burrows and pollen studied
Research described unusually large Red Crag burrows and recovered pollen from relatively unoxidised sediment, adding evidence about the marine environment and nearby vegetation.

1998 – An early bird identification reassessed
Mayr and Daniels showed that Palaeopsittacus georgei, originally presented as a parrot, did not support that interpretation.

2021 – Daniels collection enters a public museum
Michael Daniels’s exceptionally important collection of Walton fossil birds was bequeathed to National Museums Scotland, enabling extensive new research.

2022 – An early loon described
Nasidytes ypresianus was named from Walton material, adding a significant record of early loon evolution.

2024 – New galliform birds named
Research named Waltonortyx bumbanipodiides and other galliform material from the site, revealing further diversity and possible connections with Asian faunas.

2026 – A modern synthesis of the avifauna
A comprehensive review distinguished 84 bird species in the known Walton assemblage and reassessed many older identifications, confirming its exceptional scientific importance.

This account follows the local succession from older to younger. The numbered Eocene units are the historical composite log of George and Vincent (1977), reproduced in the Geological Conservation Review. They describe particular exposures, not beds that can always be followed continuously today.

THAMES GROUP

Harwich Formation

Wrabness Member

The upper Wrabness Member of the Harwich Formation forms the lower part of the exposed Eocene succession. Units 1–9 of the historical log belong to the former Division A1. They should not be confused with the overlying Walton Member of the London Clay.

Unit 1 — blue-grey clay (0.30 m)
Isolated pockets of plant material occur, with soft whitish nodules near the top.

Unit 2 — hard blue clay (0.05 m)
This thin ash-bearing horizon is locally represented by dense bioturbation structures.

Unit 3 — blue-grey clay (0.23 m)
Wood fragments and concentrations of plant debris occur within the clay.

Unit 4 — hard blue clay (0.05 m)
A second thin ash-bearing horizon may also show conspicuous bioturbation.

Unit 5 — blue-grey clay (0.85 m)
A thicker muddy interval separates the lower thin horizons from the wood-rich silty beds above.

Unit 6 — silty clay (0.40 m)
About 0.07 m above its base, a discontinuous band contains small, hard concretions, commonly formed around pyritic wood. Woody pockets and black flint pebbles occur; shelly nodules were considered likely to derive from this interval. Turtle remains were recorded in the historical account.

Unit 7 — green silt (0.05 m)
A thin greenish silt layer separates the adjacent wood-bearing clay intervals.

Unit 8 — very silty clay (0.45 m)
Wood fragments and woody accumulations are common, with small rounded flint pebbles bearing dark coatings.

Unit 9 — green silt (0.05 m)
This thin layer completes the part of the historical log assigned to the Harwich Formation.

London Clay Formation

Walton Member

Unit 10 — silty clay (0.61 m)
Woody pockets continue, and occasional larger logs occur with small nodules and black flint pebbles.

Unit 11 — grey clay (seen to 0.30 m)
This clay has little silt. Wood and nodules were recorded, although other fossils were not observed in the particular measured exposure.

Higher Walton Member beds
Above Unit 11, the historical section records alternating slightly silty clay beds around 0.60 m thick and clay beds around 0.30 m thick. The BGS recognises the Naze cliff as a partial type section exposing the lower 15 m of the member. Lignite, pyrite, fine sandy partings and burrowing are characteristic; the regional maximum thickness is not the same as the local exposed thickness.

A separate account by Cooper described at least 1.5 m of sandy clayey silt below about 10 m of silty clay with log concretions. Scours in the sandy interval reached approximately 0.30 m deep and 3 m wide and contained laminated fine sand; ripple structures and intense burrowing were also recorded. This is a complementary description of the same changing exposures, not an additional thickness to add to the numbered log.

Modern study places the important Walton bird assemblage in the Walton Member, approximately 55–54.6 million years old. Some older accounts allocated bird-bearing pockets differently, so those historical horizon assignments should not be treated as settled modern provenance.

CRAG GROUP

Red Crag Formation

Basal phosphatic lag
A major unconformity separates the Red Crag from the Eocene muds. A discontinuous lag, commonly only a few centimetres thick, contains rounded polished phosphatic mudstone pebbles, occasional boxstones and reworked fossils. Better-preserved articulated shells have also been recorded near the base. This lag is part of the Red Crag, not an additional formation.

Cross-bedded shelly sands
The Red Crag reaches about 4–5 m at the southern end of the described section and thins northwards. Iron-stained, quartz-rich sands contain abundant marine shells. Large foresets chiefly dip southwards or south-westwards, recording moving submarine sandwaves; smaller opposing sets and rhythmic bedding reflect tidal influences. Concentrations of Glycymeris shells may lie convex-side upward. Burrows include Skolithos and large structures assigned to Psilonichnus.

Upper decalcified zone
The uppermost metre or so may have lost much or all of its carbonate through later leaching. The irregular lower limit cuts across the original bedding. This is an alteration zone within the Red Crag, not a separately named member.

Later Pleistocene sand, gravel and silt
Up to about 5 m of younger sediment caps parts of the cliff. River-laid sand and gravel and finer silt or brickearth have been disturbed by cold-climate processes, producing involutions, ice-wedge structures and local deformation of the underlying clay. No unverified formation or member name is assigned to this variable superficial cover.

Water moving through the permeable Crag and gravel meets the less permeable Eocene clay, helping to create springs and rotational landslips. Slumping and beach erosion repeatedly change what is visible and mix material from different geological levels.

References
BGS: Wrabness Member
GCR: Palaeogene section
GCR: numbered Eocene section
BGS: Walton Member
GCR: Red Crag section
Mayr (2026): revised Walton avifauna