Boxstones: In search of Miocene Suffolk

Tim Holt-Wilson (UK) The date is 24 May 2014 and I am browsing across East Lane Beach at Bawdsey in southeast Suffolk. A brown lump of sandstone with a white fossil shell impression catches my eye. A boxstone. This is the first one I have ever found with a fossil in it. Looking closely, I see that the sea has abraded the shell’s outlines, although the margins have survived better than the rest, so it should be possible to identify the specimen (Fig. 1). Fig. 1. Boxstone, found 24 May 2014. Boxstones are fragments of a vanished world. They are all that remains of a lost geological stratum in Suffolk called the ‘Trimley Sands’ (Balson, 1990), although deposits of similar age are still present across the sea in Belgium and other parts of Europe. Boxstones are lumps or concretions of brown sandstone, which may contain shell fossils and – if you are extremely lucky – bones and teeth. They are beach-rolled and rounded, and typically measure between 5 and 15cm in diameter. The sand is mostly quartzose, with a rich assemblage of secondary minerals, and is cemented with carbonate-fluorapatite (a phosphate mineral) and calcite (Mathers and Smith, 2002). Boxstones can be found scattered sparsely across the shingle beaches at Bawdsey and Felixstowe Ferry (Fig. 2), and in situ as a common component of the basement beds (nodule beds) at the base of the Coralline Crag and Red Crag formations of southeast Suffolk (Fig. 3). They are eroding out of the … Read More

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Pliocene bryozoans in the Suffolk Coralline Crag

Paul D Taylor and Rory Milne (UK) 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. 1). 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. Outcrops of the Coralline Crag in Suffolk (shown as yellow).Deposition occurred in shallow water, about 4Ma, 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, … Read More

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