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 a conventional fossilizations of shelly and bony elements. The Wenlock Series offers a diverse macrofauna that includes polychaete worms (Kenostrychus), sponges, graptolites, a chelicerate (Offacolus) 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.

References

• Mark D. Sutton, Derek E.G. Briggs, David J. Siveter, and Derek J. Siveter, "Visualization and reconstruction of three-dimensional fossils from the Silurian Herefordshire lagerstätte", Palaeontologia Electronica, 4.1 (2001) (pdf file)
• Briggs, Derek E G, David J. Siveter, and Derek J. Siveter, 1996. "Soft-bodied fossils from a Silurian volcaniclastic deposit," Nature, 382 pp248-250.
• Orr, Patrick J, Briggs, Derek E G, Siveter, David J, Siveter, Derek J., "Three-dimensional preservation of a non-biomineralized arthropod in concretions in Silurian volcaniclastic rocks from Herefordshire, England", Journal of the Geological Society, January 2000 (pdf file)