Trilobites from the Iscayachi Formation (Upper Cambrian? Lower Ordovician), Cordillera Oriental, South Bolivia. Biostratigraphic implications.

CANELO, H.N.; VACCARI, N. E; SMITH, L.; WAISFELD, B.G

Fósiles y Facies de Bolivia

Revista Técnica de Yacimiento Petrolíferos Fiscales Bolivianos

Lugar: Santa Cruz de la Sierra; Año: 2016; p. 36 - 58

A study of the trilobite fauna from the Iscayachi Formation (uppermost Furongian ? lower Tremadocian) exposed in the South of Bolivian Cordillera Orientalis carried out. The analysis is focused on the Tambo Guanacuno, Cuesta de Erquis, and Quebrada de Palqui sections, and includes the revision of trilobite taxonomy with modern criteria as well as the reassessment of the stratigraphic position of some taxa. We provide comprehensive morphological information and clues for the classification of several species that, despite that were poorly-known, have been widely employed in the literature. The revision includes the following taxa: Pharostomina alvarezi Suárez-Soruco, Altiplanelaspispalquiensis Přibyl and Vanĕk, Golasaphus palquiensis (Suárez-Soruco), Onychopyge branisai Suárez-Soruco, Rhadionopleura incaica (Suárez-Soruco), Leptoplastides cf granulosa (Harrington), Angelina punctolineata Kobayashi, Saltaspis steinmanni Kobayashi, Parabolinella boliviana Juarez Huarachi, Kainella andina Suárez-Soruco, Conophrys erquensis Kobayashi, and Akoldinoidia sinuosa (Přibyl and Vanĕk). From a biostratigraphic standpoint two lower Tremadocian trilobite associations are distinguished in the Tambo Guanacuno section. The lower association is referred to the lower part of the Jujuyaspis keideli Biozone, whereas the upper association is related to the upper part of this biozone. The trilobite fauna from Quebrada de Palqui is broadly coeval with the lower association of Tambo Guanacuno. Bolivian associations are correlated with those occurring in successions exposed in the West of the Argentine Cordillera Oriental, such as Sierra de Cajas (base of the Guayoc Chico Group) and Ronqui Angosto locality. The association from Cuesta de Erquis is related to the Kainella andina Biozone (uppermost lower Tremadocian) and it is readily correlated with several sections of the Argentine Cordillera Oriental yieldingthis biozone