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Two diastems in the King Ferry Shale Member (Ludlowville Formation) are the result of local submarine erosion. These discontinuities, traceable from the Cayuga Valley to Seneca Lake, are marked by bioencrusted hiatus-concretions, and both diastems display westward erosional overstep of underlying beds. Hiatus-concretions show complex sequential histories of in situ formation, exhumation, and biodegradation. Activity of bottom organisms influenced erosion; substrate modification by infauna acted to trigger or accelerate sediment loss in a low energy setting. Both diasterns are developed along a depth related paleoenvironmental gradient; submarine erosion in this area is controlled, in part, by the presence of a gentle northwest dipping paleoslope. Juxtaposition of three conditions: bioturbation of surface muds, episodic wave or current impingement on these muds, and substrate inclination resulted in local sea floor erosion through a process of downslope sediment transport and dispersion. King Ferry diastems are termed stratomictic. Stratomictic discontinuities are erosional breaks which lack discrete hiatal surfaces due to vertical sediment mixing by infauna. They include several other examples from the New York Devonian and probably have analogs in numerous sedimentary sequences world-wide.