Revisiting the Cambrian of Miquelon Island, a French prolongation of Newfoundland’s Burin Peninsula

Abstract

The recent publication of the St. Pierre-et-Miquelon geological map by the French Geological Survey (BRGM) has highlighted some of the stratigraphic unconformities and uncertain chronostratigraphic assignations that characterize the southwestern prolongation of the Newfoundland’s Burin Peninsula. The northeastern colourful coastal creeks of Langlade (or Little Miquelon), connected across a slender sand isthmus to the northern Grand Miquelon, allows a complete reconstruction of the Cambrian stratigraphic framework, in ascending order: (i) the heterolithic Chapel Island Formation, composed of at least 150 m of variegated sandstones, shales and isolated limestone nodules and centimetre-thick interbeds, which have yielded skeletonized microfossils such as Aldanella attleborensis, “Ladatheca” cylindrica, Watsonella crossbyi and undetermined hyoliths (Anse à la Gazelle), characteristic of the Cambrian Age 2; (ii) the sandstone and quartzite-dominated Random Formation, about 130 m thick (Anse and Cap à Ross); (iii) the Brigus Formation, 15 m thick and exclusively recognized at the Cap Percé islet, comprises a centimetre-thick polymictic lag capped by a heterolithic and variegated succession of shales, sandstones and centimetre-thick limestone interbeds; (iv) the Chamberlain’s Brook Formation, 50 m thick and dominated by green shales and subsidiary reddish and blackish shales and centimetre-thick limestone nodules (Anse aux Soldats); and (v) the Manuels River Formation, more than 80 m thick and composed of homogeneous black shales bearing centimetre- to metre-scale limestone nodules and concretions infested with trilobites (Anse aux Soldats). The lowermost nodules of the latter formation have yielded a trilobite assemblage dominated by Ptychagnostus atavus and subsidiary Bailiaspis cf. howelli, Clarella gronwalli, Eodiscus punctatus, Hypagnostus parvifrons, Peronopsis fallax, Phalacroma scanicum, Pleuroctenium granulatum and Ptychagnostus ciceroides, representative of the Paradoxides davidis Zone (included in the late Drumian Ptychagnostus punctuosus Zone), whereas the uppermost nodules contain scattered olenid sclerites (Protopeltura sp.) of Furongian age. The base and top of the Brigus Formation are represented by erosive unconformities linked to gaps broadly related to a part of Cambrian Epoch 2 and the Cambrian Epoch 2-lower Drumian. Both gaps are correlatable throughout New Brunswick and the marginal platform of the southern Burin Peninsula.