Portal de Periódicos da CAPES

Trilobites de la Formación Volcancito (Miembro Filo Azul, Cámbrico Tardío) del Sistema de Famatina, La Rioja, Argentina: aspectos sistemáticos y paleoambientales

2007; Asociación Paleontológica Argentina; Volume: 44; Issue: 3 Linguagem: Espanhol

1851-8044

M. Franco Tortello, Susana B. Esteban,

Paleontology and Stratigraphy of Fossils

Resumen. El Miembro Filo Azul de la Formacion Volcancito (sierra de Famatina, La Rioja, Argentina) consiste de un tramo inferior (30 m) de margas y lutitas calcareas finamente laminadas con intercalaciones de areniscas finas, un tramo medio (85 m) de areniscas carbonaticas medianas a gruesas masivas, y un tramo superior (50 m) con pelitas que alternan con bancos de areniscas muy finas. Estudios previos sobre trilobites, graptolitos y conodontes asig- naron la seccion al Cambrico Superior-Ordovicico Inferior. El tramo inferior del miembro (Biozona de Parabolina frequens argentina, sector inferior) contiene una profusa fauna de trilobites estudiada por Harrington y Leanza a mediados del siglo pasado. Desde entonces, se han obtenido nuevas colecciones, las cuales motivan este estudio. Se reilustran polimeridos originalmente descriptos con material escaso (Onychopyge riojana Harrington, Asaphellus riojanus Harrington y Leanza, Rhadinopleura eurycephala Harrington y Leanza, Plicatolina scalpta Harrington y Leanza) y se reconsidera la identidad de varios taxones (Angelina cf. hyeronimi (Kayser), Parabolinella sp. 1, Parabolinella sp. 2, Pseudokainellatosellii sp. nov., Conophrys sp.) (los trilobites agnostidos, revisados recientemente, se excluyen del estudio). La fauna comprende varias especies endemicas. A su vez, el registro de Parabolina (Neoparabolina) frequens (Barrande) permite efectuar correlaciones con otras secciones del Cambrico Superior. La abundancia de nutrientes en el fondo marino habria favorecido el desarrollo de una comunidad de trilobites diversa, con diferentes morfotipos y habitos alimenticios. Varios taxones estaban especialmente adaptados a vivir en un ambiente con escaso oxigeno, algunos en probable simbiosis con bacterias del azufre. Abstract. TRILOBITESFROMTHE VOLCANCITO FORMATION (FILO AZUL MEMBER, LATE CAMBRIAN) OFTHE FAMATINA SYSTEM, LA RIOJA, ARGENTINA: SYSTEMATICSANDPALEOENVIRONMENTS. The Filo Azul Member of the Volcancito Formation (Famatina range, La Rioja, Argentina) consists of a lower part (30 m) of thinly laminated marls and calcareous shales with intercalations of fine-grained sandstones, a middle part (85 m) of massive middle to thick-grained calcareous sandstones, and an upper part (50 m) of shales with interbedded layers of fine sandstones. Previous studies on trilobites, graptolites and conodonts assigned the section to the Upper Cambrian-Lower Ordovician. The lower portion of the member (Parabolina frequens argentina Biozone, lower part) contains a diverse trilobite fauna that was studied by Harrington and Leanza in the 1950s. Since then, new collections have been obtained, which are the subject of the present study. New polymerid trilobites, originally described on the basis of scarce material, are re-illustrated (Onychopyge riojana Harrington, Asaphellus riojanus Harrington and Leanza, Rhadinopleura eurycephala Harrington and Leanza, Plicatolina scalpta Harrington and Leanza) and the assignations of several taxa are reconsidered (Angelina cf. hyeronimi (Kayser), Parabolinella sp. 1, Parabolinella sp. 2, Pseudokainella tosellii sp. nov., Conophrys sp.) (since the agnostoids have been recently revised, they are not included in this study). The fauna comprises several endemic species. On the other hand, the occurrence of Parabolina (Neoparabolina) frequens (Barrande) permits the outcrop to be correlated with other Upper Cambrian sections. The abundance of nutrients in the sea bottom must have favoured the development of a diverse trilobite community, which included different morphotypes and feeding habits. Several taxa were especially adapted to live under low-oxygen conditions, probably in symbiosis with sulfur bacteria.