Abstract

ZEBALLO, Fernando J.  and  TORTELLO, M. Franco. Late Cambrian - early Ordovician Trilobites from the Alfarcito area, Tilcara, Oriental Cordillera, Jujuy, Argentina. Ameghiniana [online]. 2005, vol.42, n.1, pp.127-142. ISSN 1851-8044.

The trilobites of the Alfarcito area (Tilcara, Jujuy Province, Argentina) are mainly represented by olenids, kainellids, agnostoids, ceratopygids, hapalopleurids and calymenids. The agnostoids from this region are described for the first time. In addition, some morphological aspects of the polymerid trilobites are discussed on the basis of the good state of preservation of the material. The records of Parabolina frequens argentina (Kayser), Parabolinella and Onychopyge indicate a Late Cambrian age (lower part of the eponymous biozone) for the Casa Colorada Formation. Although the Alfarcito Formation has no trilobites, its conodont and graptolite faunas have enabled us to date the upper part of the unit as early Late Tremadoc. A similar age is assigned to the overlying strata of the Rupasca Formation, in which Bienvillia tetragonalis (Harrington), Leptoplastides marianus (Hoek), Parabolinella argentinensis Kobayashi, Peltocare norvegicum (Moberg and Möller), Pseudokainella keideli Harrington, Pharostomina trapezoidalis (Harrington), Hapalopleura sp., Apatokephalus sp., Gymnagnostus n. sp. A and Geragnostus sp. are recorded. Although the faunas studied contain some endemic forms ( e.g. , Hapalopleura ), they show strong affinities with those from Europe ( e.g. , Parabolina , Peltocare ) and are therefore assigned to the Baltic Province.

Keywords : Trilobita; Latest Cambrian-Early Ordovician; Alfarcito; Jujuy; Argentina; Systematics; Biostratigraphy.