Definition of the Eifelian- Givetian Stage boundary

Abstract

The boundary for the Eifelian-Givetian Stage Global Stratotype Section and Point (GSSP) in the Middle Devonian has been ratified bq, the ICS and the LUGS and is placed in a section at Jebel Mech Irdane in the Tafilalt of Morocco. The position of the boundary was selected by the Subcommission on Devonian Stratigraphy in 1992 to coincide with the level at which Polygnathus pseudofoliatus changes to Polygnathus hemiansatus as described herein. The boundary corresponds closely a Middle Devonian division, and with the entry of the dacryoconarid Nowakia otomari. Although spores are not described from the section owing to thermal modification, the level is thought to lie below the appearance of Geminospora lemurata the entry of which has been widely used elsewhere in spore-bearing regions as a guide to the Givetian. Comments are made on the relations of the GSSP level to the associated Kacak or otomari Event