Abstract

ALBANESI, Guillermo L.  and  ACENOLAZA, Guillermo F.. Conodonts from the Rupasca Formation (Lower Ordovician ) at Angosto de Chucalezna , Jujuy Oriental Cordillera: new biostratigraphical evidence for a classic locality of northwestern argentina. Ameghiniana [online]. 2005, vol.42, n.2, pp.295-310. ISSN 1851-8044.

This contribution presents a detailed analysis of a conodont fauna from the Angosto de Chucalezna locality, at the Quebrada de Humahuaca, Cordillera Oriental of Jujuy province. At this locality, where the lower and middle parts of the Rupasca Formation crop out, the conodont bearer strata correspond to yellowish sandstones and shales. They integrate a grain and strata coarsening upwards highly fossiliferous sequence deposited on a subtidal setting (shoreface transition / upper offshore). This sequence represents a characteristic interval in the Cordillera Oriental, and the microfossils were recovered from the interbedded polytaxic carbonate coquinas. Petrographic and taphonomic analyses are carried out on these storm generated rocks. Described taxa include Paltodus deltifer pristinus Viira and two new species: Drepanoistodus chucaleznensis n. sp. and Utahconus humahuacensis n. sp. The conodont fauna corresponds to the Paltodus deltifer Zone ( Paltodus deltifer pristinus Subzone) of the Atlantic realm, which is early late Tremadocian in age. Finally, a paleoenvironmental and paleobiogeographical evaluation of this new conodont association reveals a low diversity interval and suggests assignment to the Transitional faunal realm, which involves mixed faunas in middle latitudes.

Keywords : Conodonts; Rupasca Formation; Lower Ordovician; Eastern Cordillera; Argentina.