The Upper Givetian (Middle Devonian) Subterminus Conodont Zone in North America, Europe and North Africa

Abstract

Late Givetian and early Frasnian conodont communities with Icriodus subterminus have been revised on the basis of collections from Iowa (USA), the Boulonnais and the Ardennes (northern France and Belgium), the Radom-Lublin area and Holy Cross Mountains (Poland), and the Ma'der-Tafilalt region (southeast Morocco). As a result an Icriodus subterminus Zone with a threefold subdivision is defined. The three subzones correspond approximately to the “Lower and Upper subterminus Fauna” and the “insita Fauna” commonly used in N America for the study of shallow-water platform carbonate successions.The base of the subterminus Zone corresponds to a level within the uppermost part of the hermanni Zone; the top is characterized by the occurrence of the earliest Ancyrodella taxa, Montagne Noire Zones MN 1 and the base of MN 2 or slightly above the base of the falsiovalis Zone.The diagnosis of Icriodus subterminus is amended and two morphotypes are recognized. The stratigraphic range of the alpha morphotype is confined to an interval between the uppermost part of the hermanni Zone and the top of the MN 3 Zone; the beta morphotype may range into the MN 6 Zone.The holotype of Icriodus subterminus from the North Liberty beds in Iowa is most likely a specimen that was reworked from the Cedar Valley Limestone. Icriodus cedarensis and Icriodus tafilaltensis are described as new species, and the diagnoses of Icriodus excavatus and Icriodus expansus are amended. Between the Icriodus difficilis and Icriodus symmetricus zones, an Icriodus expansus Zone is defined.

Givetian (Middle Devonian) historical bio- and chronostratigraphical subdivision based on conodonts

“…A comparable sequence of entries is observed in the Compte Section in the Spanish Central Pyrenees (Liao & Valenzuela-R ıos 2008), where icriodids cooccur with polygnathids, but in Compte the entries of I. brevis and I. difficilis are slightly delayed. Narkiewicz & Bultynck (2010) re-evaluated the Upper Givetian subterminus Zone by studying shallow-water carbonates strata of Laurussia (North America and northern Europe) and pelagic carbonates of Gondwana (Morocco). They subdivided this zone into three subzones (Lower, Middle and Upper subterminus) that correlate with the standard conodont zonation.…”

“…The Upper subterminus Zone correlates from the uppermost Upper disparilis Zone to the top of the Givetian. Correlation of these subzones with the standard conodont zonation is provided in Narkiewicz & Bultynck (2010, fig. 9) and summarized herein (Fig.…”

Primeros conodontos del Frasniense en el Complejo Maláguide de Granada (Cordillera Bética)

“…Distribución bioestratigráfica. Zona inferior de hermanni -Zona de punctata (Narkiewicz & Bultynck, 2010).…”

“…Distribución bioestratigráfi ca. Zona MN2 -Zona MN13 (Narkiewicz & Bultynck, 2010); Zona de falsiovalis (MN1) -Zona de rhenana superior (MN13) (Liao & Valenzuela-Ríos, 2012). Ziegler & Klapper, 1976 (Figs.…”

“…Distribución bioestratigráfica. Zona de rhenanus (parte superior) -Zona superior de disparilis (Bultynck, 2003); Zona de ansatus -Zona de norrisi (Narkiewicz & Bultynck, 2010); Zona de rhenanus -Zona superior de transitans (Liao & Valenzuela-Ríos, 2008).…”