EL GÉNERO NICHOLSONELLA ULRICH (BRYOZOA) EN EL ORDOVÍCICO DE LA PRECORDILLERA ARGENTINA. SU SIGNIFICADO PALEOECOLÓGICO y PALEOBIOGEOGRÁFICO

Marcelo G. Carrera

Abstract


Specimens of the trepostome bryozoans genus Nicholsonella Ulrich are described and figured. They occur in Arenigian limestones of San Juan Formation. Precordillera basin. Argentina. More than fifteen colonies were collected from a single horizou included in a cyclic succession of intraclastic to. bioclasti c grainsto.ne and skeleral wackestone. The specimens of Nicholsonella encrust skeletal remains, even the interior of some shells, and the surrounding sediment. The encrusting colony as well as the associated coarse-grained sediment suggest high energy conditions. The Arenig paleobiogeographical distribution of Nicholsonella is discussed. The occurrence of this genus shows a world-wide distribution restricted to tropical and subtropical zones.

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