An integrated trilobite and conodont biostratigraphy across the base of the Laurentian Whiterockian Series (lower Middle Ordovician) at its stratotype, Whiterock Canyon Narrows, Nevada

Abstract

AbstractThe outcrop at Whiterock Canyon Narrows, Nevada, is the stratotype for the Middle Ordovician Whiterockian Series in Laurentia. Contrasts in the distribution of trilobites and conodonts between two parallel sections at the stratotype demonstrate the presence of an unconformity separating Ibexian faunas (the historic trilobite Zone J, the more recent restricted “Pseudocybele nasuta” trilobite Zone, theReutterodus andinusconodont Zone) from overlying Whiterockian faunas (Zone L, thePsephosthenaspis pseudobathyurustrilobite Zone, theOrthidiellabrachiopod Zone, theTripodus combsiconodont Zone). The unconformity represents the erosional loss of a minimum of 10 m of shale and bedded limestone within the upper Ninemile Formation. In comparison to more continuous section in the Ibex region, Utah, the equivalent to the thinPsephosthenaspis microspinosatrilobite Zone and, possibly, the uppermost interval of the underlying “P.nasuta” Zone are missing.Illaenus welchinew species is described from the Whiterockian faunas of the upper Ninemile and Antelope Valley formations.