Middle Ordovician conodonts from the Buchans Group, central Newfoundland, and their significance for regional stratigraphy of the Central Volcanic Belt

Abstract

Conodonts have been recovered from carbonate clasts within breccia units in the Buchans Group of central Newfoundland. The assemblage is characterized by specimens of "Cordylodus" horridus Barnes and Poplawski and Histiodella holodentata Ethington and Clark. These and other species recovered suggest a Whiterockian (latest Arenig–early Llanvirn) age for the clasts. This is somewhat older than the whole-rock Rb–Sr age of 447 ± 18 Ma on volcanics of the Buchans Group. The carbonate clasts are considered to be derived from the area of deposition of the Buchans Group rather than from some exotic source. This interpretation is based on knowledge of local tectonics, inferred paleogeogaphy, and geographic distribution of the conodont assemblage. All other clasts in the breccia units are considered of local origin. If the conodonts are of local Buchans Group origin then they indicate a Whiterockian age for the unit. In view of this, current regional models for the Central Volcanic Belt may require substantial revision. A Whiterockian age for the Buchans Group is consistent with the observation that all significant volcanogenic massive sulphides of the Canadian Appalachians are of Caradoc or older Ordovician age. It is suggested that the Buchans Group is thrust southeastwards over the Victoria Lake Group, which is a probable distal facies equivalent.