Article: Taphonomy of the Eocene London Clay biota
The London Clay of Sheppey, Kent, is a grey plastic clay which was deposited in an offshore marine environment. It contains a diverse assemblage of well-preserved plant and animal fossils in concretions of either pyrite, apatite, or calcite. A diagenetic and geochemical study of the London Clay biota shows that apatite was the first preservational mineral to form, followed by calcite and pyrite. Mineralogy is strongly related to original biological composition. Only those organisms with an original skeletal phosphate content (i.e. vertebrates and arthropods) have been phosphatized. Thus a geochemical bias accounts for the preservation of the greatest detail in fossils of these groups. Early diagenetic mineralization is the only process which can halt the information loss occurring during decay. For this reason organisms preserved during the earliest phases of mineralization retain the most detail.