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In praise of a favourite fossil site: the beach from Overstrand to Cromer, north Norfolk

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Stephen K Donovan (UK)

If asked what is my favourite fossil collecting site, I would have to say the Farquhar’s Beach oyster bed on the south-central coast of Jamaica. I taught at the University of the West Indies for over 12 years and this locality was an easy drive. In my retirement I doubt if I will ever see it again – too far away and too expensive a trip – but it has a special place in my heart.

Who wouldn’t be fascinated by a bed 3.3m thick preserving articulated Neogene oysters in their life position, individual specimens being up to 400mm in length (Littlewood and Donovan, 1988; Donovan and Miller, 1999)? But, in truth, we all have our favourites, where we found a prize specimen or had a spark of realisation of a thought that proved informative. I could wax lyrical on many sites such as this.

If I had to choose a favourite site in the UK at present, my vote would have to be the north Norfolk coast between Overstrand and Cromer. There are notable sites in Norfolk that roll off the tongue, such as the Trimingham chalk, Happisburgh, the Cromer forest bed and the red chalk at Hunstanton, all of which are worthy and keep producing notable specimens. Overstrand to Cromer may not sit in the pantheon of Norfolk’s greatest sites, but it is because of its relative obscurity that it appeals. Holidaymakers apart, I have little competition from other collectors. I keep finding specimens that satisfy some of my personal interests, such as erratics, Cretaceous echinoids and modern borings.

Locality

This article is adapted from chapter 47 of my book, Hands-On Palaeontology: A Practical Manual, and chapter 20 of Fossils on the Seashore: Beachcombing and Palaeontology (see also my article, On the beach: Fossils on the Seashore).

The chalk and flint cobbles on the beach at Cromer and Overstrand are likely local in origin, derived mainly from offshore. The Chalk of north Norfolk extends from the Cenomanian to the Lower Maastrichtian (Burke et al., 2010, fig. 1); the latter is unusually young for the English Cretaceous succession (Peake and Hancock, 1961). Rafts of Chalk were thrust by glacial ice during the Pleistocene and are similarly Campanian–Maastrichtian based on fossil evidence (Burke et al., 2010, pp. 621–623).

The high ground in the field area is the Cromer Ridge, an east-west structure between Holt and Trimingham (Holt-Wilson, 2011, p. 18). Its origin was complex – during Pleistocene glaciations, glaciers ‘bulldozed’ superficial deposits to form the Ridge. Rafts of Chalk were intruded into these younger deposits by glaciers; and some Chalk rafts are seen between Overstrand and Cromer. Superficial deposits are prone to landslides and cliffs may be unstable, so take care.

The beach at Overstrand is about [NGR TH 249 410]; that at Cromer, east of the pier, is about [NGR TH 227 420] (Figs. 1 and 2). Although dominantly sandy, the beach also has numerous pebbles and cobbles, the majority of which are locally derived from the Upper Cretaceous, including cobbles of flint and, less commonly, chalk. The Cromer Museum is worth a visit, with a fine display of local geology and fossils.

Fig. 1. Outline map of the north coast of Norfolk between Cromer (C), Overstrand (O) and Sidestrand (S), after Donovan (2010, fig. 1). The dark arrow indicates the author’s point of access to the beach. The stippled area is between the low water mark and cliff top; it includes both the beach (groynes are indicated) and slope of the cliffs. Principal roads are shown as solid lines; railways are shown as trellised lines.
Fig. 2. View from the beach between Overstrand and Cromer, north Norfolk, looking west towards Cromer and the pier (after Donovan, 2022a, fig. 2). Note the very numerous cobbles and pebbles of chalk and, mainly, flint on the beach.

Figured specimens are deposited in various museums except where not collected (see captions to Figs. 3-12). Museum prefixes are: Naturalis Biodiversity Center (sic), Leiden, the Netherlands (prefix RGM); Natuurhistorisch Museum Maastricht, the Netherlands (NHMM); and the Natural History Museum, London, UK (NHMUK).

What to look for

Or, more accurately, what I look for. This locality satisfies three of my interests: pre-Ice Age, fossiliferous erratics; Chalk fossils, particularly echinoids; and modern borings in Chalk erratics.

Pre-ice age, fossiliferous erratics (Fig. 3)

Glacial and fluvial erratics from this beach are mainly lithics (see The Northfolk Project: Erratics and stones on the beach). Fossiliferous erratics are rare, but include a crinoid columnal in a Derbyshire screwstone, RGM 544 455 (Donovan, 2010), and vertical burrows of possible Mississippian age (Donovan, 2011b, fig. 3).

RGM 544 455 (Fig. 3) is a chert pebble of unique morphology for this area, with moulds preserving the shapes of embedded crinoid fossils, assigned tentatively to Megistocrinus? globosus? (Phillips) and typically Palaeozoic. The only British Palaeozoic cherts rich in mouldic crinoid debris are Derbyshire screwstones (Mississippian).

Fig. 3. An erratic from the north Norfolk coast between Overstrand and Cromer (after Donovan, 2010, pl. 3). Derbyshire screwstone (Mississippian), RGM 544 455, with external moulds of two large crinoid columnals, Megistocrinus? globosus? (Phillips). Coated with ammonium chloride. Scale bar represents 10mm.

Thus,I presume that RGM 544 455 originated from the White Peak of Derbyshire. At least three Neogene formations in the Overstrand area are each known to contain a small proportion of clasts of Carboniferous cherts (Green and McGregor, 1990; Rose et al., 2001; Moorlock et al., 2002): the Wroxham Crag Formation; the Overstrand Formation; and the Holkham Till Member of the Holderness Formation.

Chalk fossils, particularly echinoids (Figs. 4C, D, 5C, D and 6-10)

Chalk is exposed offshore on the sea bed and as glaciotectonic rafts emplaced in the cliffs (see above). The beach is sandy, with many flint clasts and rather fewer cobbles of chalk. Fossiliferous clasts of the Cretaceous, both chalk and flints, include sponges (Donovan, 2022b; Figs. 4A, B, and 7 herein), belemnites (Donovan and Lewis, 2010; Figs. 4A, B, 8 and 9 herein) and echinoderms (such as Donovan, 2012, 2013; Figs. 4C, D. 5C, D, 6 and 10 herein).

Fig. 4. Chalk fossils from the north Norfolk coast between Overstrand and Cromer. (A, B) Two surfaces of a kidney-shaped Chalk pebble from the beach at Overstrand, RGM 544 413 (after Donovan and Lewis, 2010, fig. 1). Look carefully and you will see the belemnite in section (top right in A, top left in B). The clast and belemnite guard have been bored by Recent sponges, Entobia isp. cf. E. laquea Bromley and d’Alessandro. (C, D) Irregular echinoid Galerites sp., RGM 621 012 (after Donovan, 2012, fig. 3A, E). (C) Apical view. (D) Oral view; peristome (centre) and periproct (posterior) occluded by flint. Specimens uncoated. All scale bars represent 10mm.

Other echinoid species are few and rare (Donovan, 2012; Figs. 4C, D and 6 right). The diversity of Chalk echinoids is low. For example, until recently, I had never found a Micraster (Donovan, 2022a; Fig. 6 right herein) between Overstrand and Cromer. Echinocorys is not common, but is the most often encountered of the Chalk echinoids (Donovan, 2012; Figs. 5C, D, 6 left and 10), preserved as calcitic tests, and flint steinkerns (= internal moulds) and external moulds.Most likely, the large size and robust tests of Echinocorys make it more obvious,and is more likely to be preserved of the Chalk echinoids.

Fig. 5. Recent borings from the north Norfolk coast between Overstrand and Cromer. (A, B) Gastrochaenolites ornatus Kelly and Bromley, RGM 617 814, in Chalk (after Donovan, 2011a, Figs. 2, 3, respectively). (A) Part of the boring, broken into three pieces by a person unknown. (B) Latex cast taken from the restored specimen. Coated with ammonium chloride. (C, D) Echinocorys ex gr. E. scutata Leske (after Donovan and Lewis, 2011, fig. 3a, c). (C) RGM 617 803, apical view, densely infested with Recent sponge borings, Entobia isp. (D) RGM 617 804, the apical surface has been largely abraded away; the most prominent boring is the base of Gastrochaenolites isp. Specimens uncoated unless stated otherwise. All scale bars represent 10mm.

Flint is particularly common on this beach. Chalk is a white, fine-grained limestone with relatively minor occurrences of flint (= chert), a secondary deposit. The relative proportions of these rock types are reversed where they are reworked as beach clasts. Between Cromer and Overstrand, clasts are dominantly flint, and chalk is a minor component of the beach load. This is because flint is harder and more durable than chalk. Chalk clasts are ground down by flint in the coastal zone (Donovan, 2021b).

Fig. 6. Upper Cretaceous Micraster? (right, NHMM 2021 010) and Echinocorys scutata ex. gr. (left, NHMM 2021 011), both in apical view (after Donovan, 2022, fig. 4) for comparison. Both echinoids retain their shape, but most surface details have been lost due to corrasion. From the beach between Overstrand and Cromer, north Norfolk. Specimens uncoated. Scale in cm and mm.

Sponges, many originally siliceous, are common in flint cobbles. A typical example is preserved as a well-rounded, elongate flint clast (Fig. 7). The sponge was possibly vase-shaped and likely oriented parallel to the long axis of the clast, whose shape it may have influenced during corrasion (that is, corrosion+abrasion). On one side of the sponge is a planispiral shell (Fig. 7), probably a serpulid worm (Proliserpula ampullaceal (J. de C. Sowerby); see Jäger, 2012).

Fig. 7. A coiled shell encrusting a vase-shaped sponge (NHMM 2020 028) (after Donovan, 2022b, fig. 2). The sponge is preserved in flint (irregularly-shaped atrium towards top) in lateral view, with an enigmatic coiled shell in intimate association in the lower half of the specimen. The coiled shell is most likely the serpulid Proliserpula ampullacea (J. de C. Sowerby). Specimen uncoated. Scale in mm and cm.

A second specimen in flint is an incomplete belemnite rostrum preserved as an external mould, tapering towards a distal point (NHMM 2020 029; Fig. 8, right).The longitudinal section is off-centre. The rostrum is intensely bored close to the surface, with borings coarsely cast in flint. Borings are slender, straight to curved and apparently unbranched, but cross-cutting. Belemnites in flint are commonly incomplete, but are nonetheless easily identified as such. Although imperfect, the belemnites in Fig .8 (left) and 9 are likely Belemnitella sp.

Fig. 8. Belemnites (after Donovan, 2022b, fig. 3), Belemnitella? sp. (Left) NHMM 2020 030, partial belemnite rostrum preserved in calcite. (Right) NHMM 2020 029, external mould of partial belemnite rostrum preserving a dense infestation of borings, Trypanites? isp., in flint. Specimens uncoated. Scale in mm and cm.

Modern borings in Chalk erratics (Figs. 4A, B, 5, 11 and 12)

The three common borings found at this site are allochthonous, all marine and derived from offshore. They are similar to those that occur widely around the North Sea coast of England (Donovan et al., 2019; Donovan and Harper, 2025).

Fig. 9. Belemnitella sp. preserved in flint at the main bus stop for services to Cromer, High Street, Overstrand, north Norfolk (after Donovan, in press b, fig. 1). While a battered specimen, the crystalline calcite of the body fossil and the shape of the external mould confirm this as a belemnite. Not collectable. Scale in mm.
Fig. 10. Echinocorys sp., specimen on beach near Overstrand (after Donovan, in press a, fig. 6). Specimen in flint clast, partly exhumed, echinoid enclosed and infilled by flint, but retaining a calcite test. Not collected. Scale bar in cm and mm.

Caulostrepsis (Fig. 11) is a U-shaped boring, long and slender, with a central vane. It is produced by spionid polychaete worms of the genus Polydora (Bromley, 2004, p. 460). These borings have a figure-of-eight to slot shape in section. Gregarious accumulations commonly have borings of a similar size; solitary Caulostrepsis may be larger and inhabit oyster valves rather than lithic clasts (Donovan, 2017).

Fig. 11. The Chalk boulder NHMM 2024 008 (after Donovan, 2024a, fig. 2). This orientation shows the side from which the Gastrochaenolites turbinatus Kelly and Bromley originated, the borings being gently conical and expanding into the rock from this position. Small worm-borings with a slot-like to figure-of-eight section of Caulostrepsis taeniola Clarke are apparent, but partly concealed by shadow in the bottom right corner. Scale bar in cm and mm.

Entobia (Figs. 4A, B and 5C) is the product of boring sponges, principally members of the family Clionaidae. Differences in the style of preservation and changes to sponge colonies as they grow to maturity can radically change the form (Bromley and d’Alessandro, 1984). Surfaces are initially perforated by numerous apertures; shallow corrasion reveals the intricate three-dimensional structure of the sponge borings (Figs. 4A, B and 5C).

Gastrochaenolites (Figs. 5A, B, D, 11 and 12) is large and may be several centimetres in length. The boring is club-shaped. Most Gastrochaenolites are the spoor of endolithic bivalves (Kelly and Bromley, 1984). The club-shape is most clearly seen if a complete boring is cast in, for example, latex (Fig. 5B).

Fig. 12. Taphonomy of Gastrochaenolites from north Norfolk: nestlers and encrusters (after Donovan, 2024b, fig. 2). (A) (left). NHMUK PEI 5592, base of a large Gastrochaenolites encrusted by serpulid worm tubes. (B) (upper right). NHMUK PEI 5586, valves of the nestling bivalve Hiatella arctica (Linné) removed from a Gastrochaenolites isp. (Beedham, 1972, pp. 188-189; Kelly, 1980); right valve is the upper. (C) (lower right). NHMUK PEI 5568, worm tubes made from grains of sand and sediment stuck together, likely by a sabellid polychaete, a post-mortem invasion of a boring. Scale in mm and cm.

References

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Bromley, R.G. 2004. A stratigraphy of marine bioerosion. In: McIlroy, D. (ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publication, 228: 455–479.

Bromley, R.G. and Alessandro, A. d’ 1984. The ichnogenus Entobia from the Miocene, Pliocene and Pleistocene of southern Italy. Rivista Italiana di Paleontologia e Stratigrafia, 90: 227–296.

Burke, H., Phillips, E., Lee, J.R. and Wilkinson, I.P. 2010. Imbricate thrust stack model for the formation of glaciotectonic rafts: an example from the Middle Pleistocene of north Norfolk, UK. Boreas, 38: 620–637.

Donovan, S.K. 2010. A Derbyshire screwstone (Mississippian) from the beach at Overstrand, Norfolk, eastern England. Scripta Geologica Special Issue, 7: 43–52.

Donovan, S.K. 2011a. The Recent boring Gastrochaenolites ornatus Kelly and Bromley, 1984, in a Chalk cobble from Cromer, England. Bulletin of the Mizunami Fossil Museum, 37: 185–188.

Donovan, S.K. 2011b. Aspects of ichnology of Chalk and sandstone clasts from the beach at Overstrand, north Norfolk. Bulletin of the Geological Society of Norfolk, 60 (for 2010): 37–45.

Donovan, S.K. 2012. Taphonomy and significance of rare Chalk (Late Cretaceous) echinoderms preserved as beach clasts, north Norfolk, UK. Proceedings of the Yorkshire Geological Society, 59: 109–113.

Donovan, S.K. 2013. Curiouser and curiouser: more on reworked Echinocorys (Echinoidea; Late Cretaceous) on the beaches of north Norfolk, eastern England. Swiss Journal of Palaeontology, 132: 1–4.

Donovan, S.K. 2017. Two forms of the boring Caulostrepsis taeniola Clarke on Queen Victoria’s bathing beach, East Cowes. Wight Studies: Proceedings of the Isle of Wight Natural History & Archaeological Society, 31: 98–101.

Donovan, S.K. 2021a. Hands-On Palaeontology: A Practical Manual. Dunedin Academic Press, Edinburgh.

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Donovan, S.K. 2022a. A beachcomber’s bonanza, or just another Micraster? Geology Today, 38: 143–146.

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