Ammonites of the Ampthill Clay, Lincolnshire

John P Green (UK) The Ampthill Clay Formation of the UK, of Late Jurassic (Oxfordian) age, represents a series of highly fossiliferous marine mudstones that form part of the Ancholme Clay Group in North Lincolnshire (Gaunt et al, 1992); but are almost unexposed in the county other than at an excellent exposure of the Ringsteadia pseudocordata zone at South Ferriby Quarry (SE 992204). Therefore, this shortage of natural exposures means that any information, which can be obtained from other exposures in this county, is of the utmost significance. Minor stream exposures at Kingerby Beck, North Owersby in North Lincolnshire (TF 0519 9340) have revealed a rich and well-preserved fossil fauna. These minor exposures have been placed by Gaunt et al (1992) within the Amoeboceras glosense zone, therefore lying at a differing stratigraphical horizon to the South Ferriby Quarry. Also, in contrast to the latter locality, the fossils exhibit a much higher degree of preservation and are therefore easier to collect. Fig. 1. Kingerby Beck, North Owersby. Minor exposures of the Jurassic Ampthill Clay. Unfortunately, biostratigraphical bed-by-bed collecting is largely impractical at Kingerby Beck, due mainly to the very minor nature of the exposures; indeed, the majority of fossils have been collected from patches of clay exposed on the stream bed. The Ampthill Clay Formation, where exposed, is present as undifferentiated pale grey mudstones, with scattered calcareous concretions. It is these that are the major source of the prolific and well-preserved fossil faunas, particularly ammonites. Some of these concretions are very … Read More