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

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

Fósiles y Facies de Bolivia

Sincronía Diseño

Lugar: Santa Cruz de la Sierra; Año: 2018; p. 36 - 58

Trilobites from theIscayachi Formation (Upper Cambrian ? Lower Ordovician), Cordillera Oriental,South Bolivia. Biostratigraphic implications. A study of the trilobite fauna from theIscayachi Formation (uppermost Furongian ? lower Tremadocian) exposed in theSouth of Bolivian Cordillera Oriental is carried out. The analysis is focusedon the Tambo Guanacuno, Cuesta de Erquis, and Quebrada de Palqui sections, andincludes the revision of trilobite taxonomy with modern criteria as well as thereassessment of the stratigraphic position of some taxa. We providecomprehensive morphological information and clues for the classification ofseveral species that, despite that were poorly-known, have been widely employedin the literature. The revision  includes the following taxa: Pharostominaalvarezi Suárez-Soruco, Altiplanelaspis palquiensis Přibyl andVanĕk, Golasaphus palquiensis (Suárez-Soruco), Onychopyge branisaiSuarez-Soruco, Rhadionopleura incaica (Suárez-Soruco), Leptoplastidescf granulosa (Harrington), Angelina punctolineata Kobayashi, Saltaspissteinmanni Kobayashi, Parabolinella boliviana Juarez Huarachi, Kainellaandina Suarez-Soruco, Conophrys erquensis Kobayashi, and Akoldinoidiasinuosa (Přibyl and Vanĕk). From a biostratigraphic standpoint two lowerTremadocian trilobite associations are distinguished in the Tambo Guanacunosection. The lower association is referred to the lower part of the Jujuyaspis keideli Biozone, whereas theupper association is related to the upper part of this biozone. The trilobitefauna from Quebrada de Palqui is broadly coeval with the lower association ofTambo Guanacuno.  Bolivian associations arecorrelated with those occurring in successions exposed in the West of theArgentine Cordillera Oriental, such as Sierra de Cajas (base of the GuayocChico Group) and Ronqui Angosto locality. The association from Cuesta de Erquisis related to the Kainella andina Biozone (uppermost lower Tremadocian)and it is readily correlated with several sections of the Argentine CordilleraOriental yielding this biozone.