Lesurien supérieur de Bear River (zone de Meguma, Nouvelle Écosse): Faune, biostratigraphie et implications paléogéographiques

Abstract

The faunas described in this paper have been recovered from three horizons in the upper part of the White Rock Formation, cropping out on both sides of the Bear River estuary, Meguma zone, Nova Scotia. They include: 1) vertebrate micro-remains, identified in thin sections in a level of limy sandstones, intercalated into the silty beds which compose most of the formation: they include scales and debris of Acanthodians but mainly a good number of Thelodus parvidens scales (Agnatha, Thelodontida), a characteristic taxon of the North Atlantic realm in Upper Silurian times; 2) three crinoid species, two of which new, corresponding to forms which show affinities with upper Silurian species from Soviet Union and Poland; 3) organic microfossils among which some spores and numerous chitinozoans among which Eisenackitina lagenomorpha from the upper Ludlow and lower Pridoli and Urochitina urna restricted to Pridoli layers. The occurrence of such faunas at Bear River lead us to discuss the paleogeographical relationships between the Meguma and Avalon zones and the major cratons (Laurentia, Baltica, Gondwana) of the peri-atlantic realm in Upper Silurian times. A close paleogeographical relationship between the Meguma zone and northern Europe during this period is proposed.