“I have been greatly disappointed … [owing to] sand, sometimes two to three feet in thickness, or the tide not leaving the shore sufficiently exposed; so that a stranger might conclude that there were no fossils to be procured at Bracklesham”.
The Sussex geologist, Frederick Dixon, writing about Bracklesham in 1850 warned readers with these words and it is no different today. Exposures of the richly fossiliferous Palaeogene sediments, which comprise the Bracklesham Group (Eocene), come and go unpredictably with the tides and weather. On a good day, extensive shell beds, around 46 million years old, cover the beach and sharks’ teeth may be found by the hundred. On a bad day, Dixon’s quote is all too true.
Fig. 1. Location map for Bracklesham Bay, West Sussex.
Bracklesham Bay is located seven miles south of Chichester in West Sussex, on the south coast of England (Fig. 1), at the eastern end of the syncline known as the Hampshire Basin. To the north, beyond Chichester, the ground rises to the Cretaceous chalk hills of the South Downs, while, to the south, across the waters of the Solent, the Isle of Wight stretches across the horizon. It is often said that if you can see the Isle of Wight, it is going to rain. If you can’t see it, then it is raining. This is a fair warning to anybody planning a trip here – this balmy stretch of coast, even on a sunny day, takes the full brunt of south-westerly gales and temperatures can fall dramatically in the evening around low tide (Fig. 2).
Fig. 3. A family fossil hunt near Bracklesham car park.
The Palaeogene geology is only exposed around the coast as, inland, much younger Quaternary deposits blanket the West Sussex coastal plain right up to the foot of the South Downs. There are no cliffs (very safe for young children) and loose fossils can be collected almost as soon as the tide falls sufficiently (Fig. 3), although exposure of the fossil beds depend on having a good low tide and no cover of beach sand (Fig. 4). The best low tides usually occur around 6am and 6pm, plus or minus an hour or so. Therefore, trips are best planned for late afternoon. When conditions are good, the site can produce some fantastic finds.
The Bracklesham Group sediments are predominantly soft, silty clays and sands that were deposited between approximately 50 and 45mya (the Turritella Bed has been radiometrically dated at 46.4 ± 1.5myrs). This was a time of minor sea level changes, with coastal sediments alternating with shallow marine sediments. It is divided into four ‘Formations’. The Wittering and Marsh Farm Formations are characterised by coastal sediments (including marsh, lagoon, tidal flats and tidal channel deposits). The Earnley and Selsey Formations are characterised by sediments of shallow marine origin. These are the most fossiliferous parts of the succession. Reconstructions of the palaeogeography indicate a large, shallow bay, with land some 50km to the west, drained by one or more fairly substantial rivers and covered by lush vegetation, reminiscent of today’s tropical rain forests. Mangrove palms fringed the coastal areas and offshore beds of sea-grass thrived for at least some of the time. The sea was no more than 10 to 30m deep, with a water temperature of around 18°C. This higher sea temperature was partly due to a warmer world climate, as well as continental drift, because, at this time, southern England lay at a latitude of around 40ºN.
The beds dip to the south and strike E-W, providing a full sequence, from the underlying London Clay Formation in the northwest at the entrance to Chichester Harbour, to the very youngest beds at the tip of Selsey Bill in the southeast. Much of this coastline has been designated a Site of Special Scientific Interest (SSSI) for its Palaeogene geology. The most fossiliferous parts of the sequence occur around Earnley and Medmerry, which are best reached from Bracklesham and Selsey, respectively. I usually recommend Bracklesham for a first visit, as the preservation of the fossils is generally better and they can be found washed up on the beach, even when there are no exposures. Around Medmerry, collecting is generally dependent on actual exposures being present.