Coral encrusted concretions: a key to recognition of a ‘shale on shale’ erosion surface

Coral encrusted septarian concretions have been found along an obscure diastem within the Penn Yan Shale Member (Genesee Group, Upper Devonian) near Canandaigua Lake, New York. These hiatus‐concretions (sensu Voigt) are found associated with an erosional discontinuity surface in the shale. The restriction of coral growth to exposed concretion and wood found on the erosion surface, indicates a differential substrate preference exhibited by these animals. Diagenesis, both prior to and following this erosion event, produced various physical structures whose time of formation can be estimated from observed cross‐cutting relationships with one another. An erosion‐related feature establishing an early‐diagenetic age for septarial fractures within concretions is described, and the origin and significance of the diastem is discussed.