Occurrence of Cyclusphaera scabrata in Achiri (late middle-early late Miocene?, Bolivian Altiplano): Paleogeographical implication

摘要

A palynological assemblage including the extinct araucarian dispersed pollen, Cyclusphaera scabrata, was ana-lysed from the Achiri locality, Bolivian Altiplano. The fossil-yielding locality of Achiri is located in the Pacajes Province, La Paz Department, in the northwestern Altiplano, Bolivia. The Achiri locality is very well known by the fossil vertebrate faunas recovered from the Mauri Formation (M6). The palynological samples come from fine-grained and plant-rich lacustrine levels lower in the same unit. An age between late middle to early late Miocene? was inferred for the palynological association studied, based on local stratigraphy and radioisotopic ages obtained higher in the series. The retrieved association is mainly represented by angiosperms; although gymnosperms, bryophytes, ferns, and fresh-water algae are also documented. Compositae are the most abundant group within angiosperms, and Polylepis also occurred but in low percentages. The presence of C. scabrata in the Bolivian Altiplano expands the taxon distribution outside northern South America and provides additional ev-idence to infer timing and distribution routes of conifers, restricted toward the tropics during the latest Neogene. Its occurrence supports a paleoelevation of no more than 2000 m for the northern area of the Altiplano in agreement with previous results. Compositae of Fenestrites type and Polylepis occur earlier in Bolivia and C. scabrata later, comparing their occurrence in miocene microfloras from low to mid-latitudes of South America.