Suffolk Coralline Crag bryozoans

Britain is not richly endowed with fossiliferous Pliocene localities. However, the Red and Coralline Crags of East Anglia make up for this deficiency in the sheer abundance and quality of their fossils. Whereas the Red Crag, famous for its gastropods and bivalves, takes its name from the colour of the sediment, the Coralline Crag is named for its ‘corallines’. But what exactly are these? Despite the name, which suggests corals or perhaps coralline algae, the corallines of the Crag are actually bryozoans, popularly known as ‘moss animals’ or ‘sea-mats’ (see Issue 12 of Deposits: Bryozoans: more than meets the eye). In fact, the Coralline Crag is a bryozoan limestone and represents a rare example of a non-tropical limestone in the British geological record.

The main outcrop of the Coralline Crag runs between Gedgrave near Orford in the south, to Aldeburgh in the north, forming a low ridge almost parallel to the Suffolk coast (Fig. 6). There are also small outliers further south at Sutton and Tattingstone, but the latter is now submerged beneath a reservoir. Lateral equivalents of the Coralline Crag can be found in Belgium and Holland (for example, see Bishop & Hayward 1989).

Fig. 1. Pectinid shell from the Coralline Crag encrusted by numerous bryozoan colonies.

Deposition occurred in shallow water, about 4mya, along the margins of the ancient North Sea. Giant submarine dunes – sandwaves – swept the fragmented remains of bryozoans and other shells along the seabed, leaving behind the spectacular, cross-bedded carbonate sands (calcarenites), seen at localities such as Crag Farm, Sudbourne (Fig. 7). Detailed descriptions of this and other localities can be found in Balson (1999).

Fig. 2. Globular Coralline Crag bryozoan Meandropora.

Bryozoans galore

The bryozoan fauna of the Crag is internationally famous. In the same year that Charles Darwin published the Origin of Species (1859), his friend, George Busk, brought out a monographic account of the bryozoans of the East Anglian Crags. This described 117 species of bryozoans from these deposits.

Although a full revision of Busk’s work has never been undertaken, we now know that there are at least 134 bryozoan species in the Coralline Crag. Further species doubtless await discovery. However, Busk’s Palaeontographical Society monograph still remains a key reference on the bryozoans from the Coralline Crag, despite changes to many of the generic names.

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Fig. 14. Sudbourne Park.

Paul D Taylor and Rory Milne

Paul Taylor is a bryozoan researcher in the Palaeontology Department at the Natural History Museum, London, and past President of the International Bryozoology Association. Rory Milne is a volunteer helper in the Museum, concentrating on the bryozoan collection from the Coralline Crag.