Lower Devonian (Emsian) rugosa of the Izarne Formation, Montagne Noire, France

Abstract

An account of the systematics, biostratigraphy, ecological setting and the biogeographic implications of rugose corals from olistoliths of the Cabrières area is given. Corals of the lower member of the Izarne Formation are dated by conodonts asgronbergiZone age, and includeLythophyllumsp. indet.,Calceola sandalina(Linné),Tryplasmasp. A,Breviphrentis rohartiPedder new species,B. exiguaPedder new species, andAqishaphyllumsp. A. Corals from the middle member of the formation includeFrechocystis pertinaxPedder new genus and species,Calceolasp. undet.,Rhizophyllumsp. aff.R. ukalundenseHill and Jell,Tryplasma enormePedder new species,Tryplasmasp. A,Breviphrentissp. A,Platysmatophyllum halleriPedder new genus and species,Pseudochonophyllum sentumPedder new species, andIzarneophyllum barroisi(Frech) new genus. No age significant conodont has been recovered from the middle member. However, scutelluid trilobites, which, together with other trilobites, evidently used the underside of Izarne corals for shelter during molting, provide correlation with conodont sequences in the nappe domain to the north and southwest of Cabrières. From this line of evidence, the middle Izarne coral fauna is deduced to benothoperbonusZone age. The association of a variety of benthic trilobites, all with large eyes, provides evidence of a photic zone environment for the middle Izarne corals.Rugose corals from the Izarne Formation belong to the Old World Realm and have nothing in common with similar age Rugosa of the Eastern Americas Realm. This implies that the dissolution of the boundary between these realms, which occurred in the Middle Devonian, did not begin before latest Emsian time.