Wenlock Series Lagerstätte
The Silurian "Lagerstätte" preserved in the limestone Wenlock Series of Herefordshire, England, offers paleontologists a rare snapshot of a moment in time, about 420 Mya. In the formation, layers of fine-grained volcanic ash punctuate a sequence of carbonate muds that were accumulating in a marine environment on the outer continental shelf. In this fine-grained matrix, soft-bodied animals and delicate, lightly sclerotized chitinous shells are often preserved in three dimensions, as calcitic fossilizations within calcareous nodules. Calcitic fossilization is an unusual feature. The lagerstätte, discovered and first published in 1996, provides a wider representation of  organisms than conventional fossilizations of shelly and bony elements. The Wenlock Series offers a diverse macrofauna that includes polychaete worms ("Kenostrychus"), sponges, graptolites, starfish, a chelicerate ("Offacolus"), a stem-group mandibulate ("Aquilonifer") and a vermiform mollusc ("Acaenoplax"). On the microscopic scale the diverse microfauna includes abundant well-preserved radiolarians. The delicate Wenlock fossils are difficult to separate from split sections, so Mark Sutton and his team have devised a method of serially grinding sections; from digital photographs three-dimensional "digital fossils" are reconstructed from datasets.