Abstract

In various recent studies the area of Saint-Germain-de-Joux (Ain Department, France) has been used as a reference to define a new major sequence boundary that was added to the Exxon cycle chart and assigned to the Kimmeridgian-Tithonian boundary. Within the reef complex of Saint-Germain-de-Joux the new sequence boundary SB 140 is believed to be represented by the horizon overlain by a black-pebble conglomerate. A comprehensive survey of the biostratigraphical data already published proves the age of the discontinuity to be in fact late Kimmeridgian, Beckeri Zone. Following recent refinement of the vertical range of the species of the genus Gravesia, the Kimmeridgian-Tithonian boundary is now placed within the Gravesia beds in the lower part of the bioturbated limestone ("Calcaires a tubulures") of the Couches du Chailley Fm.

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