FIRST RECORD OF ORDOVICIAN BRACHIOPODS AND GRAPTOLITES FROM CORDÓN DE LILA (PUNA DE ATACAMA) NORTE DE CHILE

Abstract

Brachiopods and graptolites are reported for the first time from the Quebrada Grande Formation exposed at Cordón de Lila, south of the Salar de Atacama. The stratigraphic succession, over 1000 m thick, consists of conglomerates interbedded with sandstones and shales. The calcareous microconglomerates and calcarenites laying near the base of the unit have yielded the brachiopods Paralenorthis sp., Monorthis transversa Benedetto, and Mollesella? sp. The three taxa have been recorded elsewhere in the Sierra de Famatina, western Argentina, from beds of well-constrained Arenig age (O. evae -B. navis conodont zones). The graptolite fauna recovered c. 300 m above the brachiopod levels consists of Tetragraptus sp. and Cryptograptus? sp., suggesting a Yapeenian-early Darriwilian age (approximately late Arenig-early Llanvirn of the British Series). This discovery is significant as it constitutes the westernmost occurrence of Ordovician marine faunas in the Argentine-Chilean Puna region, and supports a paleogeographic connection between the western Puna Basin and the Famatina volcaniclastic belt.