Fulletby brickyard: A classic locality in the Upper Jurassic Kimmeridge Clay of Lincolnshire

John P Green (UK)

The Upper Jurassic Kimmeridge Clay Formation in Lincolnshire crops out along the western edge of the Lincolnshire Wolds scarp (Swinnerton and Kent, 1981) and many years ago was formerly exposed in many small workings that exploited the Lower and Upper Kimmeridge Clay Formation for brickmaking. The once famous brick pits at Market Rasen (TF120888) and at Stickney near Boston (TF342570), both richly fossiliferous and the source of many historic museum specimens (in particular, ammonites and marine reptiles) have long since closed and the sections are no longer accessible.

Nevertheless, I have located another former, now largely overgrown brickyard, near the village of Fulletby (TF298734), situated just under five kilometres north of Horncastle. Whilst largely overgrown, small exposures remain of the Upper Jurassic Kimmeridge Clay Formation. The Palaeontographical Society lists the locality of Fulletby brickyard in its 1954 publication, Directory of British Fossiliferous Localities. It identifies the exposures present as belonging to the ammonite zone of Pectinatites wheatleyensis, and it was indeed thanks to this publication that I was able to discover this locality. The locality is also briefly discussed in Swinnerton and Kent (1981).

The exposures that remain are intermittent and scattered, but shallow excavations made by me have revealed a sequence of richly fossiliferous mudrocks, which has allowed a rare opportunity to inspect and collect specimens from this rarely exposed horizon at this little known geological locality in Lincolnshire.

The mudstones consist of finely laminated, bituminous, shaly clay, which have revealed an abundant fauna. Small bivalves (Lucina miniscula) are abundant throughout, with sporadic small oysters and brachiopods. The restricted benthic (bottom dwelling) fauna, together with the bituminous, shaly nature of the enclosing matrix, are indicative of a stagnant, oxygen poor, sea floor environment. Nonetheless, the nektonic (or swimming) fauna that would have frequented the main water column are well represented by abundant cephalopod, fish and reptile remains. Ammonites are very common, although mainly flattened, and they appear mainly to belong to the genus of the fine ribbed perisphinctid, Pectinatites spp.

Many septarian nodules, both large and small, often divided by mineral veins, are present within the clay; ammonites are found crushed (but strengthened) within these concretions and are also found partly three dimensional. In the clays, they are mainly crushed. When found fresh, an original layer of the nacreous shell remains, which makes for very attractive fossils on extraction. However, I have not observed any pyrite at Fulletby, which is readily observed at many other Kimmeridge Clay localities.

I have also not found any belemnites, but most interestingly, apparent remnants of related cephalopods, closely allied to the true belemnites, have been discovered. These appear to represent a belemnoid, possibly Belemnoteuthis – a squid like animal without the calcitic guard of belemnites, that occurs in the Oxford and Kimmeridge Clay Formations (Page and Doyle in Martill and Hudson, 1991). The remains I found consist of flattened phragmocones, with apparent remnants of the pro ostracum also evident. Obviously, the nature of the original sea floor greatly facilitated the preservation of such delicate organic remains.

In terms of the vertebrate faunas, well preserved fish teeth have been recorded at this locality (as mentioned in the Palaeontographical Society guide of 1954) but, more excitingly, I have also observed marine reptile remains. On examining a crushed Pectinatites ammonite at home, I discovered a small, partial, but well-preserved vertebra on its reverse, originating from either a marine crocodile or a plesiosaur. These tantalising glimpses of saurian remains leave little doubt as to the probable presence of more substantial remains awaiting discovery.

This account of the faunal diversity of Fulletby brickyard is an indication that historic sites, often overlooked by modern geologists, can sometimes still yield interesting geological information. A century ago, most villages and towns had their own local brickyard supplying the local demand, before the advent of the mass production of bricks forced their closure. It is all the more important, therefore, that such sites, which can be rediscovered by the amateur geologist, are documented and the fossils collected, as we shall never return to the days of the local brickyard.

About the author

John Green is an amateur palaeontologist from Lincolnshire. He holds a Post Graduate Certificate in Geology from the University of York, as well as a BA Honours degree in Scientific Illustration from the University of Lancaster. He has published many articles on local geology and given presentations at geological conferences, in addition to published works in several scientific papers. He can be contacted at: john72green@gmail.com.

References

Page, K and Doyle, P. Other cephalopods. In Hudson, J and Martill, D (Eds) 1991. Fossils of the Oxford Clay. The Palaeontological Association Field Guide to Fossils: No. 4. The Palaeontological Association, London.

Palaeontographical Society 1954. A Directory of British Fossiliferous Localities. The Palaeontographical Society, London.

Swinnerton, HH and Kent, PE 1981. The Geology of Lincolnshire. Lincolnshire Naturalist’s Union.