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

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Abstract
Coral encrusted septarian concretions were found along an obscure diastem within the Penn Yan Shale Member (Genesee Group, Upper Devonian) near Canandaigua Lake, New York [USA]. 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.