Lower ordovician sequence and conodonts, mount patriarch, north-west nelson, new zealand

Abstract

Limestone beds forming the upper part of Mount Patriarch, 1687 m, are named the Summit Limestone and are described from the section exposed on the northern ridge of the mountain. Trilobites from the basal beds and conodont faunas from the lower and upper parts of the limestone indicate that the age ranges from latest Tremadocian to early Arenigian. The development of carbonates in the Lower Ordovician of New Zealand is thus established for the first time; this contra;ts markedly with the only other known New Zealand rocks of this age—the graptolite-bearing slates and quartzites at Aorangi Mine and Preservation Inlet and turbidites of the Greenland Group at Reefton—and suggests a pattern of Lower Ordovician sedimentation in belts of contrasting facies. Twenty form-species of conodonts, from 6 samples, are described. They are grouped into two faunal assemblages, one correlated with the Drepanodus? gracilis-Scolopodus sexplicatus Zone of Australia, of basal Arenigian age, and the other with an undescribed faunal assemblage from Australia representing a later horizon in the early Arenigian. © 1975 Taylor & Francis Group, LLC.